I have 1 reason and one reason only...
To run Half-Life, Dark Forces II, and Drac's Shadow (a suped up clone of Castlevania II).
Many old Win95 games are problematic in XP and 7, plus I'm looking for ways to avoid having a dedicated Windows machine in my house.
Besides, the next Amiga Commodore had planned was supposed to be able to run Workbench, Mac OS, and Windows...
I'd say AROS (bugs aside) is the closest to achieving that dream in particular, though I'll be happier once MorphOS is converted to Arm or X86 and will have faster hardware available to pull off such feats as well! MorphOS is just solid all around.