Some aquatic vegetation might be good for the pond. Rooted aquatic vegetation does provide habitat for some small aquatic animals, which adds to the food chain.
Vegetation also provides small fish with places to hide from larger predators.
The problem with weeds is uncontrolled growth. Also, predators become thin because they are not able to prey on the forage species. Aquatic weeds can be controlled by manual, chemical, and biological means. Manual control of species like cattails is practical when they first start to colonize a pond. Woody vegetation along the dam also can be controlled manually.