it's certainly not a pose people'd use that often in real life, barring things like martial arts positions (since I know nothing about them). I can understand its appeal as far as pixel art goes, at least. lets you show off more of the subject's body and pose, even when he's supposed to be facing something perpendicular to the viewer. (at least, that's why I'd use it.)
it's a lot more normal in your second example, where the subject is just looking at something; that's more believable, and that doesn't look like an uncomfortable angle for the head. the first, which I'm assuming is a sideview battle pose, is kind of extreme (since the body is legit aimed at the viewer 100%, while the head is almost a quarter-revolution away from that).
a lot of the time it seems like a case of clumsy posing, but I've seen it used really well, too. I'd say it's a valid type of pose as long as the spriter gives sufficient thought to it.