And in answer to that, as long as you don't schedule it to scan whilst playing a game, they shouldn't affect performance
Most people have 8GB Ram+ now as well, so it's not a resource hog either.
Example of a site we have all probably used - speedtest.net
http://www.invincea.com/2013/02/pop...mised-by-exploitdrive-by-stopped-by-invincea/
Angler EK using multiple 0 day (ie. no patch from vendor available) attacks.
http://threatpost.com/latest-flash-0day-under-attack-possible-ties-to-group-behind-angler-ek/110847
Sure AV isn't perfect but it's far better than nothing.