Let me tell you, there has been many a time as I sat in front of my RCBS, 'Case Prep' machine with a thousand rounds, or so, moving across the table from left to right that I asked myself this very same question!
Do primer pockets - really - need to be cleaned; and should flash holes be reamed? Well, after more than twenty years and God, only, knows how many thousands of rounds: I DON'T THINK SO! (I've, probably, brought on early arthritis in my hands from all this handling and re:handling of shells, so this conclusion is hard wrought on my part.)
Here's the way I've come to see it. For precision rifle work, the answer is, 'Yes!' Primer pockets should be brushed out and flash holes should be uniform in size and shape. But then again for a match rifle or hunting reloads: case necks should be turned; cases should, also, be trimmed to proper length; and mouths should be nicely beveled. This kind of precision rifle shooting requires reloaded brass to be allocated to, 'strictly practice rounds' after 10-12 reloads.
The same rules that apply to automatic rifle rounds, also, apply to pistol and revolver ammunition. Simply stated: frequent primer pocket cleaning and uniform flash hole sizes are not, all that, important. If the case has been fired less than 10 or 12 times, with a relatively clean primer mixture, it is not necessary to clean out the pockets. Sure, occasionally, there will be a high primer; but a dirty pocket is not, necessarily, the answer here. It could be something, else, like head deformation, or a, 'soft' or an angled press fit.
In my experience, 'loose' primer pockets are much more of a problem than dirty ones. On many presses you can, often, spot this, 'loose fit' problem during the primer seating phase of the operation. GENERALLY SPEAKING if you spin the loaded cylinder on a revolver to rotate all six(?) rounds; and, also, learn to perform, 'opposite-hand, slide-top sweeps' as well as that old: 'pop-the-mag' and, 'rack-the-slide' routine on your auto, then, you should be fine with your reloads MOST of the time.
If you're shooting a GLOCK, (with the brave exception of a handful of, 'real men') none of the experienced reloaders I've talked to reload past the 8th time; and, for whatever it's worth, I always keep my reloads in their own batches of, about, a hundred rounds each; and, for all other handguns, after about 12 reloads, or so, I don't fool around with the cases, anymore, I throw them out and buy new brass.
Does this reloading scheme work? Well, after more than 25 years, I still have both eyes and all my fingers! I have had a few duds over the years, though: one bullet stuck in the barrel, two or three light charges, and about a hundred, or so, primer failures; but I've never overcharged a round; and I've, yet, to experience my first GLOCK, 'kaBoom!'
In one sentense: Primer pocket cleaning is not critical to the creation of FUNCTIONAL ammunition reloads.