LED Spectrum Question

I'm going to have two rooms, a flowering room and a veg room.
We all know veg needs blue and flowering needs red.
My question is what is the benefit of buying a big unit that mixes spectrum?
Is there a reason to mix spectrum? Would it be a better idea to buy one light that is all blue and a light that is all red?

Most of the respectable LED companies have units that mix spectrums, because both flowering and veg plants still need a little from each spectrum. However, some lights are flower specific. I would recommend asking this question in the LED users thread. But to answer the question, you'd be better off buying 3w systems that mix spectrums, and maybe flowering specific for the bloom room.

Personally I've vegged with a unit that was for flowering and it worked great.