Electric razor with a 1 or 2 is best kept for nether-regions. As Pete mentioned, going down to skin is a total bitch when it starts to grow back in.

As for my face, it's kind of a "whenever" sort of thing. Like, if I notice something starts growing sideways for some dumb reason (as my hair tends to do), I'll trim it up. I take the straight razor to all of it at least once a month though, just to freshen it all up. My sideburns go insane if I don't keep those boys in check once in a while.