If your garage door chain is too loose, it can cause issues with the operation of your garage door. It is generally better for the chain to be slightly loose rather than tight. When the door is open in "manual mode," the chain may sag too much, but it should be fine when the door is closed. If you notice that the chain hangs loose again after tightening, it could be due to a problem with the bolt or nut that secures it. Checking and adjusting the chain's tension is important for the smooth functioning of your garage door.