If loading for a single shot, you don't need to crimp.
If loading for a magazine rifle, fill the magazine up and shoot all except the round that was in the bottom of the magazine. If the bullet wasn't pushed further into the case with recoil, you don't need to crimp; if it was pushed in, then you do.
If you are going to crimp a bullet with no cannelure you can use the Lee Factory Crimp Die with no problem.