Ummm... wouldn't your OAL stay the same? Your seating die would give the same OAL everytime... how much bullet exposed would be different with different case lengths. Might screw up the headspacing with certain calibers that space off the case lip.
I really don't see a need to trim pistol cases. Maybe 357 Sig, but I don't know. IIRC you trim rifle brass since the head space is off the shoulder the neck can be too long and be forced into the forcing cone and cause major pressure problems if it is too long.
I load for 380, 9mm, 45acp, 45AR, 38spl, 357mag, 44mag, & 45colt pistol rounds. I trim the 357, 44,&45 only because I want the cases the same length when I crimp. I take the shortest case from however many I'm loading and trim all the cases to that length on a Lyman trimmer. Most of my cases are shorter after a few trips through the sizer die.
I've checked lots of them as a part of "keeping every thing the same", but later on when I got over all that stuff, I've found out that it probably not necessary. I have cases on their 4th reload , and they still haven't shown an increase in length.
I'm thinking its because they have a taper crimp, and the pressures aren't contained in the brass as long that way?
Can't say as an expert, but thats just an opinion.