User blog comment:Shinhwalee/Guide to Power Leveling Heavy Cruiser (CA) in World 3-2A/@comment-140.0.203.51-20150319162631/@comment-3502824-20150322065920

You don't need to but it increases its accuracy so that it can sometimes hit the enemy even at 0 morale.

The BBV is just there for 2nd shelling phase.