It depends on the sub-unit. Having done half-rectangle triangles (or whatever the term is for rectangles that are 2 different fabrics on the diagonal) the way a pattern told me to, one needed to be super accurate with the cuts. I gave up after a handful and broke out my Deb Tucker split recs tool. So for some things I "Tuckerize".
Very recently I took a class using the Stripology ruler to do some subunits like flying geese, and boy, was that fun to learn! I'll put that into play next time I have lots of geese in a pattern.