Many companies recommend scanning your computer weekly.
Personally, I only run about twice a month, sometimes less. This is for two major reasons:
I can tell if my system is infected by any sort of malware/grayware
I know what to look for in suspicious sites, and I take caution around them
If you are a user not familiar with the computer, and download frequently, or you are connected to a network, then (especially if its a network with kids on it) I would highly recommend scheduling your computer to scan Every day, every other day, or every three days.
If you are just a basic user, who doesn't excessively download, and knows how to pretty much avoid anything catastrophically bad on the internet, then I could go with the companies recommendation and schedule a scan once a week.
A key idea though:
If you leave your computer on anyways, you might as well have it scan daily when not in use like Patio does, since your not loosing any of your time or computer resources.
Always make sure you have a resident/on-access scanner (a scanner that scans files when they are opened) Its not necessarily to have the scanner on high (meaning it scans everything no matter what), but, usually a good idea to have it set to "normal" scanning.
Running your scanner on High constantly isnt a bad practice, but, can waste system resources. If running a scanner on high doesnt slow things down too much for you, then that is probably the best option. On slower computers, running on high can waste a lot of time for you, the user.
Still, nevertheless, always back up your data in the even that you get an extremely malicious virus that destroys all your data because some person wanted to make you miserable.
