The thing is, there is no stipulation that the subproblems be any "smaller" than the original problem. They just need to be instances of the same problem combining together in a manner that solves the original problem.
Yes, I can think of a case where how it may be used to solve some problems on a M x N grid, where in you could move in either directions top-left to bottom-right Or vice-versa.
I perhaps used smaller where subproblem may be a more optimal use.
