I seem to get high conversion (mash) efficiency with my traditional BIAB.
Or at least I do since I read the Water book and pestered the heck out of AJ and Martin. Before then it oscillated between 70% and 83%.
It is NEAT to get a high number, but all I really care about is a)not having a conversion problem, b)being consistent.
If my conversion was consistently 80%, I would simply adjust for that in BIABACUS and buy more grain.
I think FV mash is a great concept if you can apply it.
Remember, the traditional sparging techniques developed because of technological and physical limitations to the lautering process. (I don't have a footnote for this, it is my inference. Perhaps they needed wilserbrewer bags.
)
It stuck around for tradition and comfort, like many human institutions have.
But IMHO, it's nice to do away with unnecessary frippery when you have the luxury of being able to step back and go, "huh, do I really need that?"
Also, production breweries chase efficiency on wort extraction. My buddy, a brewer at Gordon Biersch, sings the praises of AB's consistent quality product (though he doesn't normally drink such boring beer). Now I know we are not in the business of beer, but when you maximize use of your materials (while avoiding tannins and off-flavours), that's just good process.