When a top is tucked into a bottom that has belt loops, the outfit looks better to my eye when it is worn with a belt. Empty belt loops look naked to me, and I desperately want to add the coverage. It adds a polished touch to the outfit. I guess my preference makes sense because I bat for Team Polished. Team RATE might think differently.
I prefer belt loops that are filled by the belt. That is, with a belt that has a similar height to the loop (right).
I also like skinny belts looped into wider belt loops (left), but do have a thing for filling out belt loops to their fullest! Skinny belts are a lot less bulky and I do understand their appeal, but they can slide around and fall askew. This drives me batty when the belt is a high contrast colour.
The semi tucked look is an interesting case. I still prefer the look with a belt, but it can also be fine without one.
These are by no means rules or guidelines, just stylistic preferences. Do you like the look of exposed belt loops? Or do you prefer it when visible belt loops are finished off with a belt.