You can bump with a Redding 'body die' as well(they're cheap).
Headspace amounts to the distance a chambered casehead could be from the boltface when driven forward by primer strike. On ignition, the case expands and grabs/seals against the chamber walls beginning at the case mouths and working it's way back to the webs. With this, the case is stretching back to the boltface, slamming against it.
This leads to thinning of case brass back near the webs and in extremes casehead separations(it rips right off, leaving most of the case stuck in the chamber). Also, extremes(like SAAMI + high pressure loads), is bad for pretty much anything you can think of. There is just no good in it.
By far most cartridge designs, with accurate loads, cause cases to stretch a tiny amount with each cycle, eventually causing difficult closing bolt turn. By the fifth reload without shoulder sizing, you will probably be at a point of needing bumps. From this point on, that brass will need bumps(~2thou).
When you FL size brass that stretches a lot on firing back to SAAMI, you are overworking brass, leading to constant trimming. A lot of reloaders do this, I would not. It makes no sense to me to go this route.