This is one of those things where you will get all kinds of answers. Some will not clean at all and some will go to the other extreme. I guess you would say that I go to the other extreme.
I use vibratory cleaners with a type of corncob media. I also add Rooster Bright periodically to the media.
Before I do anything I first de-prime with a universal decapping die. I feel that this lets me feel the tightness of the primer pocket. It is kinda of hard to feel if you are full length resizing at the same time. This way I don't end up finding out a pocket is loose after I prime it. Waste of my time and a primer.
After decapping I then run the cases through the vibratory cleaner before going any farther. I also run them through the cleaner after resizing and before priming. After each cleaning I blow each case out with compressed air inside as well as the outside. Before the last cleaning and blowing out I chuck up a brush in the drill press and run each case up and down on the brush. I feel that this gives me a more consistently clean necks inside and that helps with consistent neck tension.
There are other steps involved that I do but this gives you an idea when and how much I clean cases. I figure that I've got some expensive dies and an even more expensive chamber so I want nice clean cases whenever possible. Kinda gives me a warm and fuzzy feeling to see all of those bright and shiny cases during the processes I go through.;);)
I just think that I've got way more time than money so anything I can do to make my feeble little mind happy is just one more thing I do.