What to ensure before the creation of a viable spinout opportunity?

What does viable mean for TTOs, and do we have the same definition everywhere? On which grounds are TTOs advising to create a spin-off rather than out-licensing the IP or a contract-based R&D collaboration? Which are the benefits, limits, constraints and indication of the spin-out model? What are the key factors to create a well-conceived spin-off company, how to exploit and maximise the value creation?