I've found processors well worth it when feeding big, course grasses; they seem to utilize the feed better.

On finer grasses and alfalfa, I don't see the benefit, and I've had some digestive problems with the finer feeds.  Our rule now is to process the course orchard grass and unroll the other bales.

The processor gets fed on hard, dry ground.  When it rains, it all gets unrolled.