Automated tests are a form of executable Living documentation - their focus is on demonstrating the intent of the code. When following an outside-in testing approach, using representative data, then tests describe how to use the code.
Unit tests provide the path to production in the form of a quality gate - therefore if tests hinder getting changes to production, through being ridden with communicating the intent of the code, then the ability of the developer to deliver to production is compromised (Speed is a byproduct of quality)