Obama won't pardon Snowden not because Snowden doesn't have the right friends. He won't do it because it would be a politically unpopular move. Everyone can get behind pardoning someone sentenced to life for shoplifting under a three strikes law. Snowden is much more divisive.
If that were important in granting pardons, Clinton wouldn't have pardoned Mark Rich. Those politically-opposed to Obama will remain so regardless of what he does, so he couldn't care less.
In the Marc Rich case, Clinton had a pretty good idea of what the upper bound of the crime being excused was. Also: he shouldn't have pardoned Rich, is I think the consensus at this point.
What does it even mean, apart from lip service to those who disagree with their vote? Politicians don't hold personal responsibility for the fallout of their policies, so it is just rhetoric intended to neutralize your negative opinions of them.
Just what you suspect it does: nothing.
Commutation of sentences is actually much more common, particularly at the state level, because it doesn't really carry with it any indication that the person didn't commit a criminal act (and thus is less politically risky), only that the punishment was either too severe or that there's no reason to continue with it. I believe it also doesn't block further civil penalties or suits, although I'm not clear whether a Presidential pardon actually does (haven't ever seen any examples of that).
Why?
Snowden doesn't have enough powerful forces in high places that will push for the pardon. If he has friends like Jonathan Jay Pollard has, chances are he'll get it, but he doesn't.