Our lack of IP assignment waiver was red-flagged during a VC due-diligence exercise. It became a non-negotiable item, and we got all our employees to sign a waiver. Our waiver has an exclusion list similar to Google's IARC, but unlike Google we have allowed 100% of all exclusions that employees have submitted.
It did seem the VCs were far more worried about a rogue former employee somehow acquiring IP rights over our core IP than stealing unrelated work from our employees. No-one has been able to explain to me how this might happen though; I suspect it's all paranoia.
> rogue former employee somehow acquiring IP rights over our core IP
"Rogue ex-co-founder comes out of the woodwork X years later and claims they own half of your thing" is a horror story in startup land; see Facebook for an example of this. (The Social Network movie is a fictionalized depiction, but the real-world drama was sufficiently troublesome for Facebook that they initially weren't planning on engaging with the movie. Last minute they decided to rent a theater to take the whole company to see it, and
Jesse Eisenberg started helping Mark Zuckerberg with his public speaking.)
It did seem the VCs were far more worried about a rogue former employee somehow acquiring IP rights over our core IP than stealing unrelated work from our employees. No-one has been able to explain to me how this might happen though; I suspect it's all paranoia.