Some Ackley Improved cartridges are well worth the gains they provide over the standard cartridge. Other's don't do much but cost you a bunch of time and money, only to gain you 50 - 100 fps in velocity.

I've built a 223 AI and 260 AI rifles in the past, only to take them apart and sell the barrel's, dies, and brass. They just didn't do much over the standard cartridge's, and weren't worth wasting time with to me.