Damage can be caused by a lot of unfortunate incidents, some from everyday activities, some from moving, and some extraordinary moments.
Probably my most unique one was when someone brought me a cabinet part off of an electronic keyboard case that had been struck by a bullet. I didn't ask any questions. I just got to work. . . Another unique situation occurred at a church sanctuary that was being remodeled. A piece of contractor's equipment fell from high above onto the center of the grand lid.
There are two reasons to keep the sun off of your piano:
1- Allowing the sun to hit a piano will cause temperature changes that contribute to it going out of tune more quickly than if the temperature of the piano is kept constant.
2 - Long-term exposure to the sun will fade the wood. If this occurs, major refinishing will likely be the only way to correct the issue.