I just booked a B2B on the Summit in December. The first half was booked by me directly through the Celebrity people and the second half was booked via my TA but….. I was too late for my TA to transfer the first half to her. That was somewhat of a dilemma so make sure you have your TA do both parts of your B2B.
As far as advantages go, it doesn’t seem like Celebrity offers anything for B2Bs. However you do save on travel, airfare, motel etc.