If all factory rifle brass came about 0.030" shorter than trim-to-length it sure wouldn't break my heart.
Yeah, but with 30-30 where you want a nice consistent crimp for use in tube magazines, it is sure nice to have every case exactly the same length. Sure, you can cut them all to less than "trim-to" length to make that happen, but I much prefer being able to make them "right" for not particular reason.
I just began processing all of my saved once-fired 30-30 brass and noticed quite a few of the Winchester and some RP that were about .006 under trim-to length. Resizing got them a lot closer where they should be.