This is only applicable if you have Battle Mode under Wait (Not Active) and is the most common Bat.Mode used for speedrunning. Under this mode, this allows us to use what we called “Wait Tricking”. The trick makes us able to get more turns with our characters than it is intended. During a battle animation of one of your character, you can stop everyone’s ATB* by simply going into a Magic/Item Menu or by going into Steal/Tool and some others (SwdTech menu doesn’t stop people’s ATB).
The video below shows up a situation where Wait Tricking is used (Going into a Menu to stop everyone’s ATB during an animation) VS a situation where it is not used. You can see the enemy’s ATB being filled on the video (Only focus on the Middle Red Bar). This is only to visualize how Wait Tricking works and helps you understand.