Well ... a game. :-) A few years ago I was the IT Administrator for two medical universities and used Fusion since we were a VMware shop. (fully vertualized server infrastructure) I've since switched to Parallels for various reasons now that I only need a VM for personal use.
I play an old game, 11 years old now, and I do a lot of 'modding' for it. For some reason charactor textures (cloathing textrues) don't appear ... characters are simply pure black which is what a model looks like if you don't put a texture on it at all.
This prevents me from doing some of the work that I want to do, so I end up having to do the work exclusively on my gaming PC. For the odd times I travel, I like to be able to work on, or play, the game and a VM is perfect for it. Except for the missing texture issue.
So the only reason I need boot camp at all is for a decade-old came that you can buy for $5 online. :-) But I play it and work on it a lot.