A last is the solid form a shoe is built around. It is not a copy of your foot. A foot at rest and a foot mid stride are different shapes, and a shoe has to work for both, so the last adds volume in some places, holds tight in others, and allows for how the material will move once it has been worn in.
We generate one digital last per foot from your measurement file, then apply allowances by material. Leather relaxes and takes a set. Hemp gives across the weave but not along it. Wool moves in both directions. The same foot in three uppers needs three slightly different lasts, and that is applied before anything is cut.
The last is kept on file. A second pair, a different model, or a resole years from now all start from the same geometry, which means the fit you approved is the fit you keep.