I do it as a matter of consistency.
I treat it as busy work, but I do every case.
I use bad weather days and/or late evenings/early mornings to complete case prepping. This allows me to keep planned and impromptu range days free.
I like to keep a few hundred cases of each caliber prepped for a quick load session should the need arise.
Keeping cases trimmed to recommended lengths, primer pockets cleaned, flash holes uniformed allows me to maintain a bit of consistency.
There are exceptions to the trimming I do, however. That would be .38 Spl. and .357 mag cases. While I do clean the pocket's, I do not trim as I do with rifle cases. I do make periodic measurements but I cannot recall ever having to trim either caliber before the case mouths began to split.
I know fellows who only maintenance their cases when necessary and they seem to do fine with their results. I think that as long as the reloader regularly inspects the brass and conducts maintenance when needed, the level of tediousness depends upon what makes the reloader feel better.