Needless to say, you have to have enough bullet inside the case to hold the bullet firmly. That gets us into another subject called "neck tension". I once trimmed some 22-250 cases to the recommended trim length. I then decided to experiment with lighter weight bullets. I found that there wasn't enough length on the cases to hold the bullets at the overall length that I needed to keep the proper clearance (.002") from the lands and grooves. I had to set the bullets deep enough into the case to hold them. and that set the bullet way back from the lands and grooves. In those cases you can crimp, but if you're loading hot loads, be careful because crimping raises the neck tension and the chamber pressure (although slightly) which needs to be accounted for.
In my .308 cases (I have an auto loading rifle) I am limited to setting the OAL to allow my shells to be loaded into my magazine. That keeps them about .005 back from the lands and grooves. I do however, run all my loaded ammo through a Horanady Concentricity Guage to measure and adjust the run out. I even run my factory ammo through the guage. I have found the factory ammo to have anywhere from .003 to .007 run out measurement. The instruction handbooks tell you to adjust so that all the run outs measure to .002 or less. Personally I notch that up to .001 or less. It's really hard to get that down to zero.
Redding has a set of dies that hold the bullet strait while seating it, but the dies are well over $200. I don't have those dies. I would like to run a bunch through those dies, then run them on my concentricity guage and see how much better those dies seat my bullets than standard dies. Maybe in my financial future I can splurge in a set of these dies.
Another thing that affects neck tension is the case wall thickness. To get the most consistency, they all have to be the same. You need to trim them to set your wall thickness, Then you need to run them through a neck sizer that adjusts all of them to the same tension (what ever tension you desire), again, so that they are all consistently the same.
Hopes this helps you out some.