That assumes three things. #1. Product category that fits Parse (obviously if you are dependent on machine learning built on postgresql, might not be a great fit). #2. A start-up that is comfortable with that level of dependency and lack of internal knowledge. #3. A startup who considers the bulk of their value to be in interface or first-move network effect advantage (else, company Z will clone their app using parse in a few weeks after all the hard learning is done).

EDIT: For the record, I really like Parse, and am a paying customer for two CRUD mainly products.