For straight-wall autos, the time involved is most economically spent miking a sample of at least 30 resized cases to establish the range of lengths. Trim to max or midway between max and "trim-to" lengths, only those which are too long.
Betcha won't find any...
Then sort your brass into the shorter half, and the longer half. Longer brass tends to give slightly tighter groups, according to some sources. More consistent ignition from less flopping around under the firing pin strike or something like that. Use the long brass for your 50-plus yard work.
For revolvers, however, I trim after the first reload, then about every five thereafter. Do the same for bottleneck rifle I'm crimping into a channelure.
Enjoy!
Cheapo