Pretty much the question in the title. If a grad student gets bad reviews as a TA, how much does that hurt them later? How much do good reviews help? What if the situation is more complex? (For instance, bad reviews when TAing, but good reviews when actually teaching/lecturing a summer course).
Edit: I asked this question with the situation of a student hoping for a career at research universities in mind, however, I am also interested in other cases.
Edit: In your answer, please mention what your background is: have you served on hiring committees? Are you reporting just what you've heard? Were you successful/unsuccessful in a job search and were told that your teaching evals did/did not make a difference?
