As Phil mentioned you simply undo the shackle at the end of your floatline feed the clutch on and redo up. We have it permanently set up on our floatlines as 1. you never know when you might need it and 2. It makes your floatline very versatile if you want to run it at different lengths.
Here's Tanc using it on his Marlin. You can see he's shortening the line as he swims with the marlin and once he's shortened it to the minimum length it allows him to go hands free to reload his second gun.