Not sure myself–I never had a delay issue to speak of before.
I have put Clam & clam sentinel now on a 98 pentium 2 box–one running 192 ram and it chugs as it looks at each file you work on, on the other 98 box–768 ram-- no delay on programs until I use it heavily. For Avast until now I have never had any problems with it at all even with other active items.