I just use Subways.
I think in this game are many buildings just for the esthetic and have not so much use.

Our what do you think about this?

Well they serve to reduce traffic. So when you place a bus depot next to an intersection with lots of traffic (think of the annoying helicopter telling you about 'heavy traffic'), they'll reduce the amount of traffic at that intersection and a few street blocks ahead.

Bus depots are actually more efficient in reducing traffic than railroads or subways.

You can turn your city into a massive transportation bureaucracy.