The disclosure of prior agreements is to YOUR benefit as the employee / contractor. A lot of employers treat this as sort of a nod nod, wink wink situation, where they know you have prior conflicting agreements and would rather not hear about them -- b/c proving knowledge of the prior restriction is an element of tortious interference, by which a former employer can go after the next one for the employee's violation of the old restrictive covenants. As the employee, by disclosing the prior restrictions, you may insulate yourself to some extent against claims by your new employer if there's a 3-way dispute. Yes, restrictive covenants are heavily abused and I wish we didn't use them so widely. But if you're asked to sign one, there are normal areas to negotiate -- but refusing to sign at all will prevent you from advancing very far in the proprietary software industry.

I have never been asked about IP assignment (and haven't really been in a situation where it would come up). But I've actually been asked about non-competes. (By a small firm which would have absolutely walked away if I had one.)