Question on 6500 vs 2700

I just got a stealth bubbleponics with two 85w bulbs, one 6500 and one 2700. They say to use them both the whole grow. I don't understand why you wouldn't use two 6500 for veg and then go to two 2700 for flower?

Basically I'm asking - does 2700k light do any good during veg and does 6500k light do any good during flower?

A mixed spectrum can give you a little variation in final product, but if your going for max yield, I'd say go ahead and two 65's for veg and two 27's for flower.