TFA does not quite explain the logic of this and somewhat suggests it as unique when it was the norm. If you are building a church, what better metric is there than the church you are building? There is no reason to measure, you can just subdivide with very basic tools. We want the entrance to be in the center, that is 1/2 church instead of 8.385 meters and that door is 1/6 church wide and 3/4 church tall. We want windows down the sides of the church, those windows are spaced 1/4 church and are 1/6th church wide and 3/4 church high. Windows have panes and doors have panels so lets subdivide those, panels/panes 1/3 window/door.
It is more complex than that and that example assumes the church is a cube but that is the basics of it and generally there is a square in there somewhere and that square is the basic unit. We want a church with no posts in the main space and our trees produce timbers so long, that length becomes 1 square, the church is 1 square wide and 1 square high to eaves, 2 square long, roof peak is 1 square above the eaves. The wisdom of the wood (or what ever material was being used) often played a role.
Personal style in this proportional sense came down to how they used the divisions and their subdivisions and their subdivisions and what random numbers they interjected into the easy divisions, which might be suggested by the divisions and subdivisions or come from just about anything. I am building a cabinet to hold my pots and pans, I have 7 pots and pans so I will figure out a way to get 7 in there so everyone knows it is meant to hold 7 pots and pans, or at least that one random person who got obsessed with that one peculiarity of my cabinet will figure out that 7 had some sort of importance too me. Easter eggs have been with us for a long time.
People often reduce the imperial system/base 12 to the foot and its inches, but it really is this sense and use of proportion that it is built on. If you are building a cabinet for your home, there is no reason to measure, it needs to be as wide as the space it will fit in so use that as your metric, make that one square and subdivide out the rest of the dimensions. Dividers, sector and straight edge are all you need, no need to deal with the fact that the space is 4.738 whatever wide and a sense of proportion to the whole will just happen for free. Admittedly, the sense of proportion might not be the best when you are first starting out but it will have a sense of proportion that could easily not be there if you got fixated on 4.738 and rounding errors in your cad software, and you never have to measure those odd lengths.