Is there a benefit to using single guard instead of all guard?

During battles, while an enemy is attacking, the player has an option of defending. The player can defend with all characters using the All Guard command or just defend with one character using that characters corresponding Battle Button.

However, there doesn't seem to be any information that I can find relating to why someone would defend with a single character instead of just defending with all. The player can't seem to attack while enemies are attacking, nor does it seem to provide the player with any noticeable defense boosts. Maybe I'm missing something though.

So, is there any benefit to blocking with a singular character rather than just all characters?

Yes, there is. Guarding detracts from your special gauge, with All Guarding detracting way more than just with a single character.

So while in terms of damage mitigation or perfect block timers there's no difference, you'll optimize your damage and meter gain by blocking with only the correct characters.

Keep in mind that if you perfect block attacks you'll regain some meter back. So you can mitigate the disadvantage of all guarding somewhat, but it's always better to block with the correct character only.