As far as I read, it seems google maps v3 doesn't require you to create and use an API key for its usage.
But by just including the following script tag in my site (without any other JS call to maps):
<script type="text/javascript" src="https://maps.googleapis.com/maps/api/js"></script>
A warning message gets displayed in the Javascript console:
Google Maps API warning: NoApiKeys https://developers.google.com/maps/documentation/javascript/error-messages#no-api-keys
Reproduction online in jsfiddle
Do we need the API key or not? I'm confused.