[IKO] Kinnan, Bonder Prodigy
makes chromatic sphere/star, as well as the original odyssey eggs, mana neutral.
Arcum's astrolabe becomes a snow sol ring that does not cost a card. There are a fair number of artifacts that benefit from this, though I don't think you need look too much further than what we already have.
Getting to 7 mana and using the activated ability can put emrakul or griselbrand into play. I have to believe putting Gris into play, drawing 14, then knowing all your mana rocks produce 2 has to be game over.
Does not add to LED fyi, LED does not tap, it just sacrifices.
Also worth noting that it also does not add to Urza mana.