depends on your AV program I think. If you're using something that uses little resources like avast, AVG, avira, NOD32 etc. then it won't hurt. but if you're using a program that eats memory like mcafee, then it's a good idea to turn it off IMO. I don't turn mine off and I see no performance difference from when it's on or off but then again I'm using AVG and that uses maybe 2MB max.