Universal rules are hard to come by, but we all develop habits and practices based on our environments and views of probabilities. I suspect some of this is regional. I ride and drive in New England over a pretty broad range of places, and while there are enormous amounts of MUP riding, an adult riding on a sidewalk is a very rare sight. Part of the reason for this is obvious, I ride in some places where sidewalks are rare, but when I'm in places like the city I live in and the metro Boston area, I just don't see almost anyone do this, even in places where I know it's legal. I have very few places where I will jump on a sidewalk, two in fact, but there's really no safe alternative in those places.
As a general rule, sidewalks and streets wind a lot around here, so riding on a sidewalk often would involve trying to see around a curve, with really low quality pavement. As a general rule, I think you would be much more vulnerable to getting run over at a driveway, hitting a pedestrian, and being hard to see at an intersection riding on a sidewalk around these parts than riding on the street.
MUPs are special-purposed sidewalks designed to accommodate cycling, so lumping them into this discussion is just confusing the issue.