In all honesty, I've never actually connected myself to the boat with the tether (we are required only to carry it). I have been in two instances where I thought it would really be an advantage to have it - both times the boat was capsized and slowly going turtle while my sailing compadre was tangled on the 'top side' of the trampoline. The first time I didn't think to throw the tether over the hull to help hold him up (and resist turtling), the second time I did think about it but it didn't quite get to the point where it was needed.

Again, the Astral life vests have this tow line thing really figured out and have a zipper pouch tucked neatly onto the side of the vest for the tether line than remains connected to the quick release tow ring. It stays neatly contained but quickly accessable in a second or two.