On a serious note, I've found a reel very useful for wreck dives, where the anchor line isn't close enough to the wreck for us to see it when we get to the bottom. Tie off a reel (it's not recommend to TIE to the anchor line, but sometimes there isn't anything else around) and swim to where you think the wreck is. Once you get there, you can lock off the reel and lay it down, but it will give you a track back to the anchor line for your ascent, which is very reassuring.
I've used one the same way when we were diving a rock reef and the anchor didn't go down exactly where we planned. And I've heard people use them at one of our popular wall sites, running one to the edge of the wall and leaving it hanging over to mark where they came in. Any time you want a sure way home, a reel can be useful.
We did use mine as a clothesline, the last day in Mexico, though . . . And used spools to hang up wings, and double-enders to keep hangers from sliding. It was pretty funny, and I wish I'd taken a picture.