Forgive me if I'm mistaken about things. It's been years since I last opened a VtR book of any edition, so my memory might be wrong, but I remember that Humanity acts as a dice cap to your Social Dice Pool when interacting with humans.
Also, your examples are... well, it's unlikely to happen due to how extreme they are. Setting aside how difficult it is to reach, much less maintain Humanity 9+, intentionally forcing a Humanity break just because a player wants a beat is poor form. If player tries that shit on my, I'd be tossing the book at their faces. That sort of taking munchkinery/min-maxin is something I as an ST won't allow on my table.
I'm also certain that no player is going to play as a waitress at a diner for an entire month, much less devote sessions for it. Sure, I'd allow Player A to have his character work the graveyard shift in a diner, but that's relegated to background/downtime. I would probably just have them roll a Humanity Break at the start of the session, if it was important enough aka player describes, acts out the scene, and emotes. Using a session for this, having Humanity Break rolls again and again and again because a lot of people are eating is nothing more than a meaningless time waster that could have been used for something more important. By conventions of narrative detail, by Player A's character working at a diner is not important enough to consider, as such should just be glossed over.
There's also the point that if a player were to just keep on pumping his Humanity to a high level, he'd be using the experience points on something which could have instead gone to other stuff like Disciplines and Attributes.
Vampire, from my point of view, is a continued grind against the inevitable corruption into a monster. Everyday you watch someone eat food is a reminder about your lost humanity, and you can either keep on fighting a losing battle for your Humanity or descend slowly into apathy and monstrosity by embracing the Beast. If he's wasting his valuable experience to remain more human, well more power to him, and I'd certainly craft stories to support this. But having Player A go to a diner to farm beats for experience, or any other similar actions, goes against the intended theme and spirit of the game which results in a flying book to the face.