Where-clauses help break up long modules. somefunc = ... where subfunc1 = ... subfunc2 = ... otherfunc = ... where subfunc1 = ...

Where-clauses help break up long modules. somefunc = ... where subfunc1 = ... subfunc2 = ... otherfunc = ... where subfunc1 = ... where subfuncA = ... subfunc2 = ... Then the reader can instantly tell top-level concerns from implementation details, and the amount of jumping-around is reduced since those subfunctions are limited in scope.