This card increases the number of times that card(s) are sent to the Graveyard by your Lightsworns. When coupled with the Lightsworn Field spell card, "Realm of Light", this doubles the rate at which you acquire Shine Counters, and your Lightsworns will become extremely powerful in only a couple of turns.
Although this card is useful for decking cards and drawing them, this card will make you lose the duel immediately when you are required to draw and you have zero cards in your deck zone at that instance before the drawing commences.
"Garoth" is a great card to combo with "Light Spiral" if your side of the field is full of Lightsworn monsters. Including this card, you'll be banish the top eight cards of your opponent's Deck in a single turn. Beware though, if your opponent's strategy is banishing their own cards, you may be unintentionally aiding them. Another thing you need to think of is not to Deck Out yourself, since you will send a lot of cards from your own Deck to the Graveyard as well.
"Garoth" is in itself a good draw engine as it further speeds up the Deck and potentially give you an extra Hand, the only apparent drawback is that it will hasten a "Deck Out".