The Spirtual Stones were a trio set of gems from The Legend of Zelda: Ocarina of Time. They didn't add nothing to your rupees, but were mandatory items in order to advance through the game. Before The Great Deku Tree passes away he gives you the Kokiri's Emerald in a very sad moment.
The Goron's Ruby is a good bit more of a happy moment after you finish the 2nd dungeon.
I had a good laugh after you get the Zora's Sapphire after the 3rd dungeon. Princess Zora (who's a fish girl) gives it to Link almost like an engagement ring. I loved Navi's comments about that one.
But they're necessary to open up The Door of Time in the Temple of Time leading to my personal favorite moment of the series.