what uses will a stockpile planet have in galciv 3 ? Many uses if the need to have a backup planet that can support other planets through, internal trade ships, population support for Food, stockpiling of local Production and boosting output of a certain stat. 

(think of the planet, as a support carrier in a fleet, but changed to suit the planets.)

(also how will you use them, well there are a lot of dead planets around orbit, so why not start there.)

let say they can stockpile Resources if Your starbase get destroyd by a fleet of ship. 

(Function: you will still have the same number of resources Your stockpile can support up to and once used one time, you will have to reclaime it somehow.) (Not self renewal, resources.)

internal trade can send small ship to the planets and be somthing usefull to solar system that is completely alone.

dead planet use the class system in a bit different way than habital planets and Extreme worlds do and have a very different Tech path making dead planet, more of an option to Your empire,rather than having the same function of being a habital planet.

 so thats what i thought out so far, what are Your ideas that can be added.

(also the devs do have a unknown plan for those dead worlds in the future, thats why they are in the game. (as appearance for now and function will come out later.)