It's a really simple feature to add and this is crucial to inplement funcionalities based on specific animations' needs.
- Play foot steps SFX when the character is stepping on the floor.
- Create/Activate collision box in a certain moment of the animation.
- Basically, run any event when that happens.
You may suggest to just use the frame number instead. Well, this hard coding practice makes things impossible to mainten when you have tons of events using it so if you need to change the animation you will find yourself in a really bad place. Why? Because you would have to change that frame number everywhere. Using tags you just need to point that tag to the frame again. You may also suggest to just create a global variable to hold that frame number and use it in the evetns. It would work but again, there are uncountable ways of doing anything but game engines are made to facilitate and improve the game development and its workflow.