new case trimming ?
 

Is it necessary to trim all new cases down to the trim to length even if they are between the trim to and max length before loading them for the first time?

You don't have to. But I usually do. Starts everything off nice and uniform.

It doesn't hurt. The mouths are sometimes a little bit off square, and are almost always sharp. Those that come in bulk are often dented, too.

I trim, chamfer and size all virgin brass. It's really no different than if it were fired.

Trimming new cases.
 

It largely depends if you're going to crimp the bullet, then case length uniformity is very important.
I found out the hard way that it's a good idea to size new cases tho. I measured powder into a batch of brand new 45 Colt cases that looked so good and uniform I didn't size them... only to find out that the bullet slipped right into them with handly any force or neck tension.