Anything that is turned on that you don't use just eats up system resources (even if it's not much they still do).
If you are planning on hooking up a printer or camera or other hardware such as that to your PS3 then leave it turned on.
If you are only going to use your PS3 for games and movies like me then turn it off - it may not make a noticeable difference but will free up that little extra space in memory.
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