Obstructed Views - Yay or Nay?

It happens quite often that someone, looking for a last minute deal, will turn up there nose at a cabin with an obstructed view. But what is an obstructed view? What’s obstructing it? Why is it obstructing it? And are there any pros or cons to an obstructed view? Fingers crossed I will try to answer some, if not all of those questions here, (with simple to understand pictures as well, because I’m just that helpful).