So I'm a bit slow. I have Jet 1642 (1.5 HP). I've had it for coming on 2 years. I turn lots of bowls at near its maximum capicity (13" to 15" range - you can never really get the full 16, at least over the bed). The lathe came with the belt on the high set of pulleys I believe (or at least I put the belt on those pulleys when I set it up). I've never thought much about low (I know, duuuhh, right?) until the other day when the motor got warm enough that it decided to take a break to cool itself off. It then occurred to me that I never spin the big bowls that fast, and some extra torque might be helpful, so after she cooled down and was ready to go again, I changed the belt to the low pulleys (took less than 1 minute). The clouds broke and the angels sang! Turning that blank was much more pleasurable with that extra torque and the motor was happier and cooler too. Anyway, I'm probably the only doofus who never thought much about the high and low configurations - happy with what seemed to be good enough in la la land - but just in case, I heartily recommend others keep it in mind for heavy work.
Happy Easter.