Why: For no good reason
I've been lusting after a Canon New F-1 since I filled out my FD lens collection. My AE-1 works perfectly and never leaves me wanting; even my AT-1 works great. So why do I want teh heavier F1? Because ... Pro models are better or some such non-sense? Because I'm a camera slut and the new F-1 seems like it would be fun.
At the other end (or rather, in the middle), I have started lusting after a Speed Graphic with a 6x6 roll back and some polaroid holders. This, despite the fact that I have a wonderful Bronica ETR-Si with the lens trio I want, and I have a Kodak 2D for when bigger is better.
So, why the speed graphic? Because it would give me a camera with movements I could use for 6x6 when I wanted them, and it has an focal plane shutter letting me play with all the barrel mount lenses I keep seeing online. I have some strange idea that I'd go to comic-con or something and shoot instant photos (ideally type-55 so I could keep the negative) of people in costumes. But the reality is, I'd probably never do it.