Interesting debate.

Personally I think if you have no intention of running AV in the background, you might as well use either online scanners, or one of those local smaller "on demand" AV packages that do the same job.

There is very reason to install a full AV with "shield" /services and all that, when all you want to do is to run on demand scans. Seems to me that even with AV resident shield off, there is still a cost in terms of drivers loading at bootup etc..