I save people with Rescue all the time. It's useful when you know a sprout is new to a dungeon and you know what always kills them and you see them about to be killed by it.

A random example. If you are in A10 and you see someone standing on the traps and triggering them over and over again, you can rescue them and thereby rescue the party.

It's useful even in the latest dungeon. There is a part on the first boss where you must be on a certain side, and if you run to the wrong side, you might be dead. You can save them and bring them to the correct side.