Loading hot loads for revolvers, roll crimps are preferred. One reason is to ensure good burn with slow (for handguns) powders, especially ball powders like H110/W296. The other reason is to keep the remaining bullets in the cylinder where they belong under the heavy recoil generated by hot loads. If the bullets come creeping out of their cases under recoil you could end up with the cylinder getting stuck, unable to turn. That can spoil your day under some circumstances.
Taper crimps are for autopistol rounds that headspace on the forward end of the chamber.
