I got lazy one time and decided not to crimp my 7.62x39 handloads. That was the last time I did that. The bullets pushed right back into the case during a string of fire, causing a jam. Neck tension just wasn't enough, and I don't have any of that asphaltum bullet sealer.
I don't crimp so hard I mess up the bullets, but I do use the Lee Factory Crimp die on my .223 Remington, 7.62x39, 7.62x45, .308 M14NM and BM-59 rounds, and .30-06 Garand and BAR loads. ALL my autoloading handgun loads, and my magnum revolver loads, get crimped.