I am from India and hence the context of this feature is in India (it might apply to others but I won't know). Cities in India like bangalore have specific parking areas. There are certain places where you can park and certain places where you cannot. There are also cases when one side of the road is used for parking on odd numbered days and other is used for even number of days. Sometimes these sign boards are also not clear
Because of these things, commuters make mistakes (including me) and pay fines. It would be good to have this information on the map as a layer (may be). An API providing information like that could be very useful.
The best thing of course would be that, I can talk out my android phone and ask it whether it is safe for me to park here (wherever I am right now). A useful answer will be fantastic for all users.