you old timers er I mean more mature folks figured it out. its for power transfer. never seen one of them thar 2 belters only ones and threes.
We had a 14inch 7.5 horse Powermatic at a shop I worked at. it was the biggest piece of junk Ive ever worked with. mainly because I think it got dropped on delivery and the prior shop manager was too apathetic to send it back. Anywho, it had three belts but was out of whack just enough to only have one actually making solid contact. That and the fact that there was a huge swale in the table that, again, instead of having a new saw sent to replace it he brought someone in to plane it flat....
Well, that lack of 2 belts I think saved my life and my hand one day when a piece of antique chestnut decided to explode on the saw as I was running it through, the work piece and my hand were wedged between the blade and the fence while part of it exploded back into me (good thing I had plenty of padding. took a shard about 2 inches into my gut) I was able to force the piece through and it actually stopped the blade... had all three been on there correctly I may have lost my hand and that piece would have shot out of there with a lot more force...