it is a combination of factors. . .
You want enough space for ppl to walk by and potentially even get a cart with shirts though. I think OSHA mandates 30" of clearance.
When setting our layout we made it so there is the absolute minimum of turning needed to place the shirt on the dryer (I think we are around 60 degrees) and minimum walking to load and unload the shirts. If they have to take a step, it's too far. Standing in one spot does not seem to work, so we have about a half step of distance. This eliminates rotating in the joints and seems to be better on the bodies.
pierre