Tests for "throw away" code, no. Tests for scripts only for me, a qualified no - if it is important the script is "correct" or subject to revision over time (hmm, isn't that anything that's not "throw away) then test can be very useful to avoid regressions. Test for public facing code, solid yes.

For code that evolves from throw away, to personal use, to "lets make this a module" it seems sensible that tests should evolve from none, to maybe some, to something that looks like TDD. Aside from anything else. casting the code in a TDD framework forces you to think about the scope of the code and how other people might use it. Thinking about usage and scope shapes the API. TDD then helps codify the API and test its utility and suitability.

Agile programming advocates often suggest that the code is the documentation, but with TDD the tests are the documentation. In a sense TDD is about writing the documentation, or at least the problem description before you write the code, and that seems like an altogether good thing to do. Thinking about what code should to before you write it can't be a bad thing surely?