for better extraction, at the expense of taste ime. Also good for peeps that have water with a high ph, but you can just use distilled water to get around that as well.
Its either an acid and less water, or lots of regular water and time. Some can stomach an acidified brew, and it can go down alot easier if its reduced. This holds true for many teas, caapi, mhrb, cactus, etc. Use just enough acid, and your brews can be not too bad tasting and mighty potent.
the acid helps break down the plant mass, and convert the mescaline and friends into water soluble salts. Since there's very little data, if any, on what salts the mescaline is naturally i tend to think its wise to make sure that there's something in the mix that will make it very water soluble.
Acetates are generally very water soluble, and excess vinegar will evaporate off. you may wish to use vinegar instead of citric acid, excess citric acid will remain in your final brew.
Just some thoughts, good luck.