Well, I've been told that the big bloom is a somewhat weak solution. And that plants respond better to the combination of big and tiger bloom. I've noticed that buds do seem to thrive with the combination. Tiger bloom has a bit more nitrogen in it. However, according to GanjaGuru, it's not such a good idea to OD on nitrogen in the flowering stage.
I am 4 weeks of 12/12 with my single female and the buds are quite large and dense for only four weeks. Not positive it has to do with tiger/big combo, but a friend of mine used just big bloom and noticed that the results weren't as good as they were when he used the combo later.
Dunno for certain, Biz. Could be a scam to sell more Foxfarm stuff. Basically, I use the big bloom with every watering and throw in a little tiger with every other watering. So far, so great. Still another month to go and at this rate, I'm going to have an incredible yield.