First of all I would suggest changing the name of the forum from "project finishing" to simply "Finishing", the project part is a given.
Here's the stupid question. Over the last couple of years or so of my woodworking adventures I have run into several brew recipes, and am guilty of using some. The question is what benefit do these provide over the ingredients used in isolation. Ease of use is the only thing that comes to mind.
To give an example a very common recipe is to use; 1/3 any oil (BLO, Tung), 1/3 thinner (naphtha, mineral spirits) and 1/3 poly. With poly included in the mix and if I were to apply two coats of such a mix, what's the point of applying oil on top of poly (which is 1/3 of the first application). Why don't we apply an oil, wait a couple days and then apply 2 to 3 coats of poly as needed.