In a restaurant I tip good especially if I'm a single for breakfast or lunch, 4 or 5 bucks isn't going to kill me instead of 2. I well overtipped right after the restaurants reopened, even for just handing out the door. Wait staff had been off for some time and most have families to feed. They would almost cry when you gave them a measly 10 or 20 bucks.
Buffets that don't have anyone come to your table during the meal for drinks or cleaning, there's no one to tip.
