I use it for extractions (phosphoric that is). Truly though I haven't noticed a big difference in yields.  I could probably shorten my cook time if it does pull alks quicker.

I have read that some people will add a bit of coke/pepsi to their brew and swear that it makes it stronger, so maybe it is an absportion thing.

I personally will never use phosphoric acid for brewing aya again. It doesn't evap so the end product is highly acidic and tastes even worse than normal aya (if that can be believed).