When is Tor Browser Bundle not enough, and you need Whonix or Tails?

Only you can answer this question as only you know your threat model. Honestly this is the best answer:

If you’re just a curious individual with a penchant for researching bizarre stuff then perhaps Tor browser or even a VPN is sufficient. If you are a whistleblower or an enemy of the state you better have a much more in depth security plan (physical and digital) than just “Is Tor browser good enough”.