I've never seen the reason for a VM running Windows on a Mac because the price is almost the same as just buying a low-end laptop with Windows 7.
For school, I needed windows and looked into Parallels and realized that for a few dollars more, I could just buy a separate Toshiba laptop. At least this allows for redundancy because if one computer breaks, I have another.
With a VM, if your Mac breaks, it breaks and that's it.
There are programs for many in school to get Windows free...check around.
Your last comment is true but the advantage is convenience of course. It's about tradeoffs and isn't any different than a person who can only have one system where if it breaks, they have nothing. It's really a silly argument to make.