It may cause harm for astronomers since streetlightings etc make it harder to observe outer space using Earth-based telescopes.
You wouldn't believe how tough it is to navigate a ship in a channel at night (looking for buoy lights) with all the background lights from growing cities competing.
Were it not for radar and gps it would really be difficult.
Coming into a port (even the fairly small ones), you look toward the shoreline trying to eyeball the buoys, and they are drowned out by all the "noise" from shore lights that are really doing a lot more than they need to do.
San Diego shifted to low pressure sodium lights to avoid harming the Palomar telescope. The lights produce a small number of known frequencies that can be easily filtered. On the downside, the light offered is monochromatic. You can not discern any colors. That makes it difficult to tell police what color of clothing, hair, skin, eyes, car or other useful data when a suspect is observed.