For what reason should the tram driver slow down when driving through a place with lowered overhead line e.g. under a viaduct?

At a location with a low overhead traction line, the current collector (pantograph) must rapidly change its operating height. Passing through at high speed generates significant dynamic forces, which can lead to damage to both the pantograph and the line itself. Therefore, to avoid a failure and ensure safety, the tram driver is obliged to reduce speed.