Technically you don't want the two limbs to do equal work, you want them to be under equal stress. This stress should be equally distributed throughout a good portion of the limbs too.
There is no such thing as perfect symmetry with a bow. You can't shoot through the pivot point (your hand), the arrow comes off above. You usually don't grasp with two fingers so that isn't symmetrical either. It doesn't matter though, as long as your bow is stable and you can hit what you are aiming at.
The most important thing is not to overstress an area of wood so it breaks down. After this, everything else is simply attempting to get the most out of a given piece of wood.