I don't know your particular situation, so it might be totally different, but I think this is commonly just a formality and a friendly chat.
It's a chance for you to meet the actual CEO (or VP or whatever in a larger company), and also for them to get to meet you in advance, instead of effectively getting "blindsided" by a new person (to exaggerate a bit).
Usually, by the time you've gotten to that point, the decision to hire you has well and truly been made. I don't know what then would need to happen for the actually rather secondary function of giving the CEO the opportunity to veto to become relevant. I'd be curious hearing about anyone who's ever experienced it (on whatever side). I guess it can be a safeguard against vastly unaligned values, but I suspect it's very rare.
But primarily, and effectively, it's usually just a meet-and-greet. And it's hard for me to blame a CEO (or VP etc.) for at least getting to anyone who's going to enter a mutual contract to effectively become part of their company.
it's usually just a meet-and-greet.
Yes, it usually is. But in this case the problem was that the CEO could unilaterally override the decision made by everyone else, so it wasn't just a meet-and-greet.
> just a formality and a friendly chat
That was not the case in this scenario. I was told I would be offered the role if I came out favorable with the CEO (did he like me or not? did I jump when the said "jump"?). To me this meant that the CEO doesn't trust the people he hires. He clearly didn't trust the hiring manager's jugement and/or respected their position. The CEO delegated a task and responsibility but then felt to have to authority to override that, which maybe he does. However, that's not a culture in which I want to operate. If I was wrong, so be it, but I saw a red flag and I made a choice.