[dnanian]

In general, I don't find it necessary to isolate system from data, so I don't partition for those reasons. If you're trying to keep some files "archived" so you can delete them, then you need somewhere to keep them (and don't forget that they're valuable too, and thus should be backed up)...

The basic rule is that you need a volume(partition) as a destination for each source you want to back up, and that volume should be used exclusively for that purpose.