I will open the sideplate on a newly purchased revolver, especially if I bought it used, for an initial inspection. I used to do an annual inspection of the internals, but after a while I realized it just wasn't necessary unless I could tell something was wrong.

It's not hard to lube the action without opening the sideplate. If you have an exposed hammer, just apply a drop of oil on either side of the hammer where it enters the frame. Turn the gun upside down and put a drop of oil on either side of the trigger where it enters the frame. Cycle the action a few times and wipe off any excess lube.

I don't remove the cylinder for routine cleaning. I did it once after a couple of years and from what I saw I could probably have gone another two years without removing it for cleaning.