In many states (including California) you will get a ticket for impeding the flow of traffic even if you are at or under the speed limit, e.g. if you are in the passing lane or not using turnout areas when on a two lane road. While you yourself don't have to speed, you do have to get out of the way of people who want to.

Ignoring everything that is happening around you, even if you are under the speed limit, is an incredibly unsafe way to drive.