This card, with "Gem-Knight Fusion", can allow you to start using the fusions without losing card advantage. You can, for example, Fusion Summon "Gem-Knight Ruby" with this card, and then Special Summon "Gem-Knight Garnet" with this card's effect. Then you can banish this card in the Graveyard to get your "Fusion" back to your hand.
If you do this, you spend 3 cards to Summon "Ruby", gain one from its Summon (-3 +1 = -2), gain one monster for the effect of "Obsidian" (-2 +1 = -1), and get your "Fusion" back for banishing "Obsidian" in the grave (-1 +1 = 0).
Doing this can net you multiple Fusion Summons per turn.
"Gem-Knight Iolite" and this card can quickly generate advantage: Fuse those two into a monster, then select "Iolite" with this card's effect. Gemini Summon "Iolite", using its effect to return this card to your hand, and return "Gem-Knight Fusion" to your hand. Not only you get a +1, if the monster you Summoned is "Gem-Knight Aquamarine", you will also bounce a monster to your opponent's hand.