Advantage moves weight closer into the hull for better weight distribution.
Advantage acts as more surface area buoyancy to better float up for shallow draft.
Disadvantage lose a little deck space.
Disadvantage fights your hulls ability to rise out of the water when you trim thus making your hull slower than an equal hull without keyslot. Motor trim tries to lift bow....keyslot keeps you planted a little more which means boat will start to porpoise. Gets worse with more speed.
Hope that helps....im sure there is more.