> but it gets in the way when you're rapidly prototyping and exploring.

If you prototype a new features for an existing system, a test let you execute only the code you actually need. This will shorten your feedback loop and allow you to iterate faster. Refactoring a test is fine. Writing a BS test just to explore a solution is fine. In my experience following a test lead practice will help you build a simpler system which will be easier to maintain.