Spyware Doctor On Guard?

I have Spyware Doctor but until now, I've been using it
without the "on guard" feature which allows it to monitor
all the time.

I run NOD32 and Sygate along with a Linksys wired router.
But I do not keep any spyware program running, although I
use them on demand, every few days (Adaware, Spyware Doctor,
Spybot).

Is it worth the resource overhead to keep Spyware Doctor On
Guard running all the time?

TIA

Louise