I should listen to 11.4, but personally I like to have enough slack in the chain so I can push up and down on the chain when its in the stand and get about 1/2-3/4 inch of movement on both the top and bottom, but not so much that there is movement when I switch from backpedaling to forward pedaling. I think that when you start to skip or skid when you're riding having that play when you switch directions makes for a hard snap on the chain, which I don't like, cus I think it puts a lot of pressure and wear on the chain. Am I making sense?