I'm pretty sure that I asked someone the other day why they used rainmeter visualizers and I now know that the answer is "because they look cool"
(thanks to the guy with a vulgar username for the image)
edit: now that I think about it I feel like I asked a more specific question, why they use them on a single-monitor setup, and in that case I still don't get that. I mean I'm gonna see this visualizer most of the time, and the clock as well. the whole reason the clock is there is so that I can tell the time in fullscreen games. ever since I found a nice little taskbar clock skin which you can see in the bottom right, I no longer technically have a need for it, but I still like the way it looks, it tells me the day of the week, and I don't have to bother taking the time to parse "6/11/16"