Added way back in Illustrator CC 2019 – this feature allows you to select, then edit multiple ‘similar’ objects at once.

First, select an object or group, then go to Select > Start Global Edit (click the button in the Properties panel or the icon in the Control panel), and other objects that have similar attributes become selected. Any changes to that first object are immediately applied to the others.

This concept can be approached in other ways, but this is so fast and easy! To learn more about how to control what gets selected, see Adobe’s help page on Global editing.