I use mine constantly. Multi effect for time based effects goes in there as well as a clean volume boost for solos (cant do that in front of a 2 channel amp on the distorted channel) and most importantly I have a 10 band EQ in the loop to really fine tune the tone. It makes a big difference in my tone with the EQ in there.
I would only buy an amp with a loop... otherwise it's just too constraining.