Rescue techniques often rely on ropes. Many involve being attached to a rope. The only safe way to do this is attaching to a quick release system. Here is a sampling of just some of the uses for a rescue vest:

• Anchor and belay - Here is a demonstration of this technique: Rescue Vest Belay
• Towing boats or gear (with tether) - Besides towing a boat on a tether, many tethers come with a really large carabineer that can clip around a paddle shaft. It is so much easier towing a paddle than paddling with two paddles placed together.
• Personal extrication - If you need extrication, you can hook a line to your tether and toss the rope to someone on shore so they can pull you in. Some PFDs also come with a Spectra loop that can be attached to for vertical extraction.
• V-Lowers and Direct Lowers - Both are real handy for fishing a rescuer to the victim. This technique can be used for pins and to recover an unconscious boater.
• Live Bait (preset and "on the fly") - This technique can be real handy for grabbing an unconcious swimmer
• Tensioned Zip line traverses
• Dragging gear which keeps your hands free

Here is a short video on rescue vest uses: Rescue Vest Uses.