The pain of keeping it around will outweigh the pain of needing it and not having it.

Quick boot into windows to help a friend test something on your machine?

• Twenty-five bajillion updates since you never logged in
• Windows "helpfully" cleaning up your Linux bootloader
• Any shared NTFS partition between windows and Linux is almost guaranteed to be left in a "dirty" state when windows shuts down, meaning you have to run ntfsfix before Linux will mount it again

And suddenly, that's where you'll be spending the whole afternoon. I agree with the others who say a VM is probably good enough.