Information feudalism. The slim possibility that you might get into an IP dispute with them later used as an excuse to make sure employees have no independent revenue-earning capability.

"It's worth $1B. Still want to buy it from me?"

"But for you, I like the cut of your jib, $100M."

I don't see a problem with this. If you put a price on that work, and they meet that price, seems like an equitable exchange.

But if they paid you that much for your IP, would you still work for them?

Well, at least for the payout period, assuming it wasn't all given in a one time payment.

Otherwise, it of course depends on what they're doing. It might be really interesting work that you get the chance to work with a lot of other very brilliant people to build something amazing.

If that's not true, then no, I'd probably go and start just writing fun open-source stuff all the time.

A lot of companies that pay by salary think business hours are 24/7.

Yeah, the added gray area here is a little uncomfortable. I have never seen a startup actually define what business hours are. What if you work late 2 nights a week, and then the third night on a side project. Could that be interpreted as business hours? Do business hours vary by individual?