My last job did this. They offered more for those who had worked there longer. People with over 15 years got about a years pay and they all took it. People who had been there under a year got nothing so they all stayed.

I was going to take then they withdrew the offer for all devs. I think a lot tried to take it and they realised no one would be left. I would have got 3-4 months pay. Loads of institutional knowledge lost though, i left anyway a few months later.

Absolutely. The ones who've resigned mentally are fine within their positions. The people with all the business connections and references will be the ones to grab the money and simply start something new. It happened at my company. I was only 3 years in, so it wasn't enough money for me to quit. But loads of good people left the company.

Depends on if the good people have better places to go, I guess. My guess is that you're probably going to lose people who have some amount of tenure, especially if you're the kind of company that gives equity that vests on a 4-year schedule. Even if you're not, people with some amount of tenure will be the ones trending towards being checked out already.

Losing people with tenure means you lose organisational memory, which can definitely be negative.

This is all to say that as an organisation, you should think twice about doing any kind of layoff. They are all bad in their own way. This just happens to be the format that is least bad for most workers, which is why I prefer it.