If your chain is tensioned too loose, you risk having it release from the guide bar during operation, which is very dangerous. It is recommended to first get your chain to its proper tension before beginning to use the machine, and then checking every 20 minutes for the first hour of use. The chain should never be allowed to sag from the bar, and should not be able to be pulled more than 1/2 and inch off of the bar at any time. If the tensioner on your saw breaks, you may lose the ability to control the tension of the chain. The tensioner may start moving freely if the screw becomes stripped. To inspect the tensioner, remove the chain cover. Next, remove the tensioner itself and inspect the screw and tension gear. These parts are easy to access, and it will be fairly noticeable if the tensioner is broken. If a new tensioner is required, refer to your user manual for the proper replacement part number.