It slows you down in 2 cases:
1) You don't set its setting sproperly
2) You don't disable real-time proection after you're done working in
dangerous environment.

If you know what to disable after you're done scanning/working in red-alert
zone, don't criticize the best AV in the world.
This thing brough my system from the grave after a severe attack at work
thru stupid boss's DSL box... the only thing that fixed my system with 80GB
of semi-government & military designs.

Learn how to use things.