ASIC Power supply requirements
Well on the die level they'll all be tied together anyway in the power grid.   That doesn't mean you only need one power and ground pin though.  You have to understand the power draw  of your chip to know how many pins you really need.  Perhaps you need many because you have a fast DDR4 bus so you need the impedance of the package to be very low (more pins in parallel lowers your impedance).  Same would apply if you have power hungry core logic.  Or maybe you need pins on all sides to help with losses from IR drop.   

There's actually a lot that goes into designing the power portions of chips and packages, but it's a broad topic.