The bottom diagram is pretty much what the expansion board is for. Do be thoughtful about current, though, as that diagram seems more appropriate to some of the driver boards that are meant for larger power distribution.
The output expander can deliver 3A, and the pro version can do 15A.
For several projects I have wired both power and data in a star pattern using the output expanders, but if using over 150 pixels total with the normal expander (750 on the Pro), make sure +5V and GND power is separately delivered through appropriate size wire, not through the expander.