Do I really need the Google Maps API key?

I am planning to release a commercial website (I have ads there and a shop) which is freely available for everybody. I want to add a google map to show some points of interest. The question is: Do I need the google api key for that or can I just use the iframe code that google gives me? Theoretically that would work, too.

I searched google, but could not find a clear answer...

Thanks :-)