Open shoving 15-20 BB's

[Bond18]

I've seen a lot more open shoving of 15-20 BB's lately from good winning players. And not just in obvious spots, such as near the bubble or when everyone behind you would be an easy all in call anyway.

I've seen it coming from like MP1 with 17 BB's in spots with a whole range of stacks behind and nowhere near the bubble or well into the money.

My questions in general are:
What kind of situations would you consider open shoving 15-20 BB's that aren't totally obvious?
What kind of hands would you be doing it with?
Which tournaments are you most likely to do it in? Higher buy in or lower and why?
Overall thoughts?