I'm sure most people already know by now, but non-prompt manual barriers often lead to prompt nukes. So if say Sasuke's barrier casting is queued after he has already launched his standard attack, he'll use his chakra cost this round, cast the barrier for free next round, and use the rest of next round's chakra to immediately launch his prompt nuke.

Very useful for Rescue Jinchuriki where guys like Tendo and Roshi can wreck your barrier.