best practice disk partioning for snowleopard and parallels (not bootcamp)

hi guys
newb question ahoy. I have been running parallels 5 on my macbook pro for the last few months but I have now decided to do a rebuild of my mbp as it is my first mac, and i have spent much time since purchase finding out what apps will work best for me and how to get the best out of it. now i want a clean start with a clean SL install and just the apps and build config i need.

before kicking off i am intrigued to know if there are any best practices around disk partitioning to get the best performance from parallels. should i keep parallels machines on a separate partition from my SL install or is there little/no advantage to this?

thanks in adv