To prevent mishaps and damage to more than the egg you’re currently working with, it is strongly advised break each egg one at a time into a separate bowl or a breaking bowl, if you will. This allows you to work with each egg and ensure it’s of the quality you want before combining it with other eggs or other ingredients and regretting an unpleasant surprise.
Things like a piece of eggshell falling in can be more easily retrieved from a single egg than several eggs. Worse yet, if for some reason you should come across the bad egg, you can simply dispose of the egg wash the dish and move on the next egg without having lost anything but the egg that was bad. This minimizes risk before transferring the egg it to your mixing bowl.
This using a separate bowl, also, applies to separating eggs; always do them one at a time to prevent one broken yolk from spoiling a bowl full of whites.