My opinion is that if you are
unfamiliar with S&W Revolvers, not handy, don't have a lot of mechanical skills and don't have the proper tools it is
far better to NOT pull off the side plate as you are certainly more likely to screw something up or ruin your Revolver.
That said, I am very familiar with them and have been smithin' them for 40 years and so doing so for me (and others here on the Forum) is second nature. As far as how often I do so depends on how much they get shot. I add or lessen the interval depending on that. If I had to guess how often I disassemble / lube / reassemble the
average Revolver I'd say somewheres around every 3 - 4 years but my EDC guns and competition guns = more often.
As far as dumping or squirting oils, and chemicals through openings in the Revolver's Frame, it shouldn't (IMO) be done for the most part and quite sparingly and ONLY with products such as Rig#2, Remoil and similar which are as thin as water and evaporate their carrier quickly
IF IT IS. If this is done with thicker oils all you will do is gunk up the inside, attract dust and unburnt powder residue, and do more harm than good. REMEMBER, with little air circulating inside the gun, what you put inside will likely stay inside and so you do NOT want anything there that can get caustic, congeal or turn into an abrasive.
IMHO different lubricants should be used for different situations. Just like a car or truck uses many different lubricants for different applications. No one lube is a do-all for every situation an application. But getting back to Side Plate removal - working on a Smith (or any gun for that matter) requires skills, knowledge and ability and is not for everyone.
Smith & Wesson will NOT tell you in their manual to disassemble your Revolver down to bare bones because they do NOT want the
liability. I have personally bought a lot of new Smiths (back in the day) and have seen them leave the Factory in various conditions - bone dry, lubricated properly, dirty and rusted inside.
They are far better off telling "Joe Public" never to take it apart and that it does not need lubrication - and in a general sense they are probably better off telling the public that instead of everyone trying to pull their products apart. Smith and Wesson Revolvers are pretty durable and will usually withstand a lot without being lubricated or cleaned inside - but I don't agree that a Revolver (or most mechanical devises with moving parts) is "lubricated for life". It is STILL a mechanical machine and there are plenty of movable and wearable parts inside. If one does NOT want to take the plunge and learn how to do this properly - seek out a good, reliable and honest Gunsmith who can easily do it for you. It's not a time consuming job and should not cost all that much.
Again, indiscriminately pouring lubricants, brake cleaners, etc. inside a Revolver through its openings is in my opinion not the way to go. If you absolutely positively can not keep yourself from doing it;
at least use a safe, thin and evaporating product like I mentioned above - and sparingly is the word! Caution - never leave chemicals of any kind inside Chamber Charge Holes to contaminate Primers.