Do you not use Microsoft security essentials snaully?

Ahh .. I see. No I use (used) Norton 360 for that.
About to change to Sophos though.

There are elements of security with AnVir (virus scanning not being one of them... despite the name), but its primary use is for system information and troubleshooting potentially rogue programs.
In fact, AnVir can be configured to replace the standard Windows Taskmanager (AnVir would popup when you hit Ctrl-Alt-Delete).
Of the information it provides, Disk Load on an individual process is one I find useful (ever wondered why your PC suddenly starts access the disk like there is no tomorrow? This can show you exactly what it is).
Its true all the information it provides it available elsewhere within Windows (even if Perfmon is needed) but, this heaps it all in one easy to follow GUI. Sysinternals provide something similar too.

You'd probably have to be into looking under the hood a little, to get any benefit from it.
I find it fascinating :)