Static maps URL without API key still works (?)

Question

I'm using images from http://maps.google.com/maps/api/staticmap

and noticed that the links work without a parameter API_Key e.g. :

http://maps.google.com/maps/api/staticmap?center=53,51&maptype=satellite&zoom=17&size=640x300&sensor=false

why should one use API_Key parameter if it's optional? Is there any reason?

Answer 1

My guess is that it works for free for demonstration within a certain limit.

As Google mentions on this page :https://developers.google.com/maps/documentation/static-maps/intro?hl=en

The Google Static Maps API Usage Limits have changed. Creating an API key and including it in your request allows you to track usage in the Google Developers Console, and to purchase additional quota if required.

Therefore, if you want to build a software using this API, it's recommended to create your own API Key, to be able to monitor your usage and avoid to be "kicked" without info.