I think it all boils down to whether it's worth it for you. If (like me) you just pick a couple bullet combinations, establish best bullet lengths for your purpose, and make a lot of cartridges with those bullet lengths - I don't think it's worth cost of a micrometer. But if you need to continuously make changes as some describe here - maybe a micrometer would help for that.
I personally think other things are more important - like my Mitutoyu dial caliper, bullet/headspace comparators & OAL gauge, magnetospeed chronometer, and competition shell holders. Good luck with whatever you decide to do.