@gearspec,

There's no answer to your question. Anything above zero is OK. Your root file system is on a chip that is way faster than the embedded MMC, so moving system files away from / serves no purpose, unless you really need the space for something else.

It's the same as with RAM. The more free RAM, the more you're wasting resources for no particular reason.

Would you buy a car with 300HP only to drive at 80km/h on a German Autobahn? I wouldn't either.