While I've heard some say that for digital "underexposure can be good" I've never seen it demonstrated. I have a sneaky suspicion that these are held-over "conventions" from slide film shooting.
That being said, exposure in scenes with a high dynamic range can be a "juggling act". As has been mentioned, you want your brightest highlights that have "meaning" to be just pushing the edge, which often means that significant parts of your composition will be "underexposed".
While that is something we have to deal with, I don't consider it a "good thing", just a necessary thing.
But, that doesn't mean that it's good to "overexpose" -- if you let a subject get too bright, well, it gets messy 'cause you can't recover the highlight detail.
If a scene is questionable as to the dynamic range, Raw becomes a great asset. For me, because I shoot in such conditions most of the time, I just leave my camera set to shoot Raw, and never switch out of Raw. The times when I have the luxury of controlled lighting with no dynamic range challenges, well, I can still shoot Raw and just make quick jpeg conversions. But if I switch to jpeg shooting for those scenes and then forget/neglect to switch back, well, I'd regret it!