Historically, devastation of the surrounding countryside, in plain view of a besieged fortress, was a very typical tactic back then of demoralizing the garrison, and/or enraging them to come out and fight in the open.

The downside to this tactic was it tended to deprive the besiegers of valuable food and shelter outside the walls, making the siege tougher for them.

But in game terms, no, I don't think any of these things occur, and detroying buildings has no effect.