I think it's about control. I want a dog who has control and knows the difference.
Like any combat sport where grappling is a component, there are times to simply hold so you maintain control and there are times to be more aggressive (shake) to further damage to your opponent.
I want a dog who maintains control and knows when to hold em and when to shake.........but never like Kenny Rogers and "fold em".

To go further, I believe some of this depends on the severity of the mouth being used as well. A dog with tremendous mouth can do massive damage without a single shake while a dog with lesser mouth may need to shake to maintain control b/c the damage he canNOT do b/c of a weak mouth.

Again, as Nut pointed out - "To many factors."