Yes a little oil goes along way, really it does. It goes a long way to assure that your firearm functions properly under most conditions, that it operates smoothly, and that it stays in fine condition both inside and out. For example I went fishing yesterday. A day or so before I went on my fishing trip I had cleaned my sidearm, and put a light coat of oil on its exterior. I also had lightly oiled some of the moving parts that the manufacturer recommends oiling. When I got to the fishing boat yesterday, I thought to myself why on earth did I bring along a pistol. I guess it was force of habit, I work while armed, travel armed, and when I am off duty from my job I am armed 99% of the time; nothing wrong with that, and nothing wrong having the pistol along with me yesterday on the fishing boat. I was thinking of taking it off, but there really was no place for me to have secured it, so in the holster, on my belt it stayed. As the few fish came over the rail it stayed there as they flopped and got water everywhere. As the fishing line went out of the guy's reel next to me the salty water again sprayed everywhere. Not lots of it but I felt it each time. As the mates sprayed salt water on the fish cleaning table and into fish buckets I again got wet. I did not give my pistol a thought for the whole trip. When I got home at the end of my fishing trip, I saw that my gun had obviously gotten wet with salt water. A tell tale dry salt stain was on my holster, and on the gun itself. I took it out of the holster, wiped it down, and guess what - Look Ma, No Rust! Nope it is not a stainless steel pistol, nope it does not have any sort of rust proof finish, heck the finish it has left is pretty worn off in many places. What it did have was a light coat of oil. It got another cleaning and light coat of oil after the trip. I looked at it this morning, still no corrosion. Now if you doubt a gun can corrode that quickly from just a little salt water, well try an experiment someday with one of your guns without any protecting oil on it. Just let it get damp with salt water, and leave it for several hours. I was on the boat for about 7 hours of actual fishing. I have had guns before this one get rusty from less exposure than that.
Besides preventing rust from forming on a firearm, a light coating of oil on some of the moving parts will reduce friction, and often will help to prevent malfunctions. I cannot even estimate how many times at the range I have seen someone show up with a dry firearm (dry as in not lubricated at all). Not only are some of the guns I see dry, they are also dirty. When the shooter who has a gun in either condition goes to fire it, that person has a much higher chance of having the gun malfunction. Often the problem will be either it will fail to eject, or will fail to feed. This is, in these cases, almost always due to the side not operating as freely as it should either because of buildup of fouling or because of lack of lubrication, or both.
Now oil may be expensive, and getting more so, but it is not too expensive to apply to your firearms to protect them and make sure they work, especially if you apply the right amount. The right amount is usually a light coating. When I apply oil to my firearms I usually do so on the out side with my finger (this may not be the best way for the gun or for my health, but it is a habit I have), with a gun cloth or cleaning patch, and with a cotton swab (being very careful that absolutely no cotton strands remain on the firearm). Once I apply what I believe is a fairly light coating, I wipe down the gun with a cloth to make sure it really is a light coating that remains. I don't wipe off all the oil - just most of it. There are a couple or a few reasons you want a light coat of oil instead of a heavy one. A heavy coat of oil can literally gum up the works. No most modern oils do not get gummy under repeated heavy use (such as the slide going back and forth) or when they heated up, but they ca be gunky if too heavily applied. When dirt is added, and oil is a dust and dirt magnet, it can get sort of gummy. You don't need too much oil attracting and holding a lot of dirt. A fine coating will also hold dirt or dust, but nowhere nearly as much as could a heavier coating. In addition the dirt comes off easier when in a fine coating, so just cycling a weapon will make some of it come off. The fact that the light coat holds less debris also means the firearm while lubricated to reduce friction is less likely to jam because of dirt.
Yes a light coat of oil means the gun will attract some dirt, but overall it usually makes the firearm operate with less friction, and protects it from corrosion. That second part, the protection from corrosion is why oil is usually better than a dry lubricant like graphite dust. Graphite and other dry lubricants do have their place. They are used in very dusty environments where oil on a firearm would possibly cause malfunctions because of the dust it would attract. Such places included areas of desert where there is a lot of fine, and I mean very fine sand. I worked in the Border Patrol for 4 years in and around Calexico, California. The area outside of Calexico is about as desert like as you can imagine except for some irrigated areas (even those are dusty when they let them dry up, or when the cattle pens are set up - nasty dust from those cattle for sure). There was a lot of dust in the air that kicked up onto my revolvers and semi-automatic pistols. I always used oil as a lubricant for my firearms while there, and never once had a problem from the dust. Still though, some who lubricate their firearms with oil claim to have major problems with dust in places like Iraq (funny others using the same oil and same firearms don't have a problem at all). Many of them prefer a dry lubricant like graphite or product like Militec-1, or Hoppes Dri-lube. I can tell you, if the soil there was anything like it was around Calexico, just using dry lubricant would make for one heck of a rusted firearm with just the moisture from sweat because of the amount of alkali in it. In a case like that, I would lightly oil the exterior, and use the dry lubricant on the inside, and clean my firearm everyday. Dry lubrication may lubricate well in a dusty area, but it offers no protection from corrosion of which I am aware; although there are claims by manufacturers that dry lubricants protect from corrosion.
Of course, before you lubricate with oil or dry lubricant, and before you apply a protective coat of oil, the firearm preferably should be clean. A good cleaning with a powder solvent is recommended after each time a self defense type firearm is fired. Some modern day .22 rimfire recommend cleaning less often; but that is usually the exception not the rule to cleaning firearms in general. I use products like Hoppes No. 9 Powder Solvent, or Hoppes Bench Rest Copper Solvent which removes fouling from copper jackets bullets in addition to being a gunpowder solvent and lead remover. After cleaning I usually (as in virtually always) apply a thin coat of Break-Free CLP. Keeping a firearm clean, lubricated and protected is worth the cost when you consider that said firearm may someday be called upon to protect you and your loved one; and the cost is minimal when compared to what it could be if you don't!
All the best,
I will probably add a cleaning video at a later date.