Reserved space

["beevis\ libero\ it" <beevis libero it>]

Hello list,
I have a doubt. When creating an ext3 fs, 5% of its space is reserved to the superuser.
I understand this should be important for /, maybe /var and /tmp.
But is it compulsory for other fs, like, say, an external disk with data?
Or it's just a heritage, no more needed? Could one safely reclaim this 5%?
I understand that no other fs (jfs, xfs, reiser) reserves some space.
Thanks for clarification