Recently I have upgraded two bus terminals.. Please tell me what are the advantages of this upgrading?

So upgrading terminals allows the limit of passengers to be increased, if your bus can take say 50 passengers but your terminal can only take 43 passengers, you will only ever been able to take a maximum of 43 passengers from that terminal.

PRO TIP: glitch in the game shows you to use gold coins without diminishing, say you have 2 gold coins, if you upgrade a terminal with 2 gold coins, you can do that and your number of coins will not go down you'll still have 2 gold coins