Depending on tank space, (always limited for me) I will grow out smaller fish with big fish. If the sizes are really disproportionate, full growns with 2" or slightly smaller, the big guys really don't seem to pay any attention or have any aggression to the little ones and their not in competition.
The older literature used to mention growth inhibiting hormones from full grown Discus effecting had that could effect growing fish. I have no idea of it's really true or not.