You should perform this scan for ALL machines once per day under normal circumstances. There is never a time when you don't do this. (During Outbreaks we increase this to once per hour if we're trying to erradicate a pesky virus.)
I would recommend that you run this with settings like "Every day at Noon -and- Run Missed Task" that way you always get it. Also, if you are only scanning memory then this scan takes about 30 seconds on a PC built in the last 3-4 years. Since it isn't touching any disk, it will have no discernable impact.