What the what? Should this valve be here?

[Nathan Grubb]

So, I'm examining the plumbing for my bathroom that sits in the joists of the basement, and I notice the valve pictured here.

One side is hot, the other is cold. From what I can tell, hot is on full-open and cold is completely shut.

The middle line runs to......the toilet.

Yep. The toilet.

Why on earth would someone plumb a valve just before my toilet, and then set it to ONLY feed HOT WATER to the toilet bowl?!?!?

Suggestions? Wisdom? Wisecracks? All welcome.