Ask HN: Tell Me About Vesting Resets

Good evening all,

I'm currently doing the first engineer deal at a startup privy to a lot of things but very clearly not a founder and not in the financial conversations. Everything is going well we've got term sheet(s) in hand and it looks like we'll be taking on some investment in the next few months.

One thing that I've heard and don't really understand is that some conversations are leaning towards vesting being reset. Understandable for VCs to ask it of founders, but can/does this tend to affect employees, and does it require consent for the employees that have already signed grant/option agreements?