The belt systems do not like going slow or towing anything. That is why a low range would be a must with a belt system. You need to be very careful towing another machine, the belts will stretch and flat spot and nothing more annoying than a vibration from a belt. They also loose performance as they wear, if used as intended they are fine and I agree with toodeep they have come a long way over the years but the basic design is the same, advances in belt material have helped. Like Jcart said they were designed to be cheap and light for snowmobiles. The engine stays at a high rpm and the clutches do the work which is fine for performance but not what I want going slow through the woods.
They are also a high maintenance system, don't let anyone tell you different. The bushings and ramps wear. We got so that we would machine our own bushing from oil impregnated bronze, they say the oil will collect more dirt but we found them better. They would still wear but did not seem to get as much noise from the clutches and seemed smoother. They usually need to be rebuilt every 2000 - 3000 miles to stay at top performance and reliable.
The new wet CVT systems they are starting to use on the cars now are a totally different bird. I do not know enough about them to have an opinion yet. I have an open mind that these new systems may be something that could be adopted for these type machines.
Don't feed the bears no matter what they tell you!