What are the giant rocks for?

Throughout the world you see these giant boulder looking objects.

You can see a few in this screenshot that dot the forest.

Do these rocks serve a purpose? I know you can blow them up with bombs, but you do not get any resource from them.

The boulders you see here are just environment details, like the trees and the like. You often run into them in caves while exploring and they can be destroyed by bombs to clear the way. The ones not in caves can also be destroyed by bombs, but they so far do not yield anything, expect a hole.

There are a different set of rocks that can be found that will surround a portal stone. these should be one-per-zone and found where a dungeon or overworld boss would normally spawn. Since they are so dinky though you really have to look for them.. They are -not- pictured in the question's image though, those are just normal boulders.