I have used it a few times to genuinely rescue someone, usually in new mechanics. I think most notable is the
Amaurot dungeon, when the person had gone for a comet on the opposite side of the room, only to realise there was no space behind it. I could see them racing towards our comet, hoping they'd get there, and when it became obvious they'd die before they reached me, I used rescue to get them the rest of the way. Got thanked for it in chat too.
It's a rare tool to use, but it does have its place.