Never. Well, maybe once.
I’ve founded 2 reasonably successful start-ups and 1 venture fund, and one thing that isn’t worth it is No Business Use Case. First, idea. Then, initial team. Or sometimes, First initial team. Then, idea.
And then it’s super important you come up with an idea you really believe can scale to $100m+ in revenue (or in a VC firm, return 8x). You of course may not hit it, but you have to believe. That way, if you come up short … you still have something.
I’ve killed a bunch of ideas, and even two “pre-start-ups” — where the team was together, even a prototype … but where I realized we’d never get to $100m+ ARR. IMHO, it’s just too hard otherwise.
Having said that, I guess “SaaStr” is a startup. It has a $7m budget including the SaaStr Annual and a great team. That had no business use case to start 4 years ago. But it could be started for free, as a hobby, part-time. A SaaS business almost always can’t.