the overhead cast is best used for distance casting, typically when you want precision casting a roll cast, or pitch is much better suited for these duties. to complete a successful overhand cast your launch angle and release point have to be correct, usually it will overrun when you cast at a downward angle, but if you cast with and out and up approach you will have much more success with the overhand cast... not saying you cannot cast down with this approach it just takes more time to learn how to, and honestly i dont see a good time or place for an overhand precision downward angled cast...
Mitch