I guess for a startup, it would hard to track what was done on company time, and what was done as a side project. For example, coding a side project on my 9-5 job would require a consent form signed by my manager to claim they had no ownership on my project. But a startup founder working on the weekend on YC's project only to realize a need for something else that needed to be coded and monetized. That's gray area of who owns the assets.