Never heard of this before. Build bigger rigs. Don't have small rigs. I honestly don't think it makes any difference. Difference is in the hardware even if they are the exact same model. Did you think of the other variables that you haven't thought about yet?
Main difference is if one goes down, you still have others mining while you fix it. But yeah, if you trust your gear, you're only saving a little bit of electricity (for my three rigs, combining would probably save 80W) by combining.