I expect the courtesy of a two week notice when someone quits
Quits vs. Fired is a whole different thing.
However, either way you run the risk of people lingering around for 2 weeks not doing their job properly because what will happen if they mess up? Gonna fire them? LOL. It can result in losing customers, causing dissent and low morale as they complain, possibly even sabotage or espionage but it's more likely when firing than quitting but I've seen it all.
Those two weeks give people time to think about things like one guy stole a customer list and tried to later steal the customers, another guy I knew sold the employee roster to a recruiter, so on and so forth. I tend to work late nights and one night I even stumbled into someone spreading out all the CFO's trash on the floor, uncrumbled, looking for something. Next day the CFO and most execs started shredding everything. You never know what could happen once they know they're out the door.
That's why I'm a big fan of just paying them for the two weeks and letting them leave immediately so it's not dragging it out. Can be inconvenient, but it's just better to make a clean cut and move on IMO.