Bend deduction
The amount a formed part is shorter than the sum of its legs, because material stretches through a bend, and the figure that sets the true blank size.
Add up the outside dimensions of a formed bracket and you get a number that is not the size of the blank it came from. Material stretches through each bend, so the developed length is shorter than the sum of the legs, and the difference is the bend deduction.
It is specific to the material, the thickness, the inside radius and the tool used to form it, which is why a general figure taken from a table is a starting point rather than an answer. The same drawing formed on a different press with a different die produces a different blank.
The quoting consequence is direct and it runs in one direction. Quote the naive blank, meaning the legs added together, and you have bought more steel than the part needs on every piece for the life of the program. On 4 bends at 0.120 material that error can be most of an inch.
It also interacts with nesting, because the blank size decides how many parts fit on a sheet. An oversized blank loses material twice, once in the piece and once in the yield.