Warren,
I connected my GPS (a Garmin 2720) to an unswitched (always on) circuit in my Fuzeblock. There are times when it's important (or at least useful) to know total elapsed time. Like on a Rally or a timed ride such as an Iron Butt SaddleSore of BunBurner.
If the GPS switches off when the key's turned off, you lose that info. Also, there are times when I want to leave it on just so it'll be right there when I'm ready to ride again. By leaving it always on, I don't have to wait through the start-up process again.
I don't leave the GPS on for overnight very often. It pulls enough power that after a few days the battery won't have enough "ooomph" to crank the engine. When I've left it on on cold nights, it put out enough heat to keep the frost melted off the windscreen on my Connie. It doesn't do that on the NT because of where I've got it mounted.