If you're new to the idea of ORICAs (Original Cards), they can be summarized as custom fake cards. Wondering what's the point of them? Here are some points.
1. Playtesting. If there's a card unobtainable for any reason, such as being too expensive or existing only in Japanese (OCG), you can use an ORICA instead, using it as a "proxy" for the real one, to playtest for fun duels.
Keep in mind though, that proxies are very much not allowed in competitive settings, such as tournaments.
2. They can be dang beautiful. Probably the main reason most people buy them, is that we try to make them really nice looking, especially the Full Art cards, which are not currently available for distribution by Konami for some reason. Aside from also being able to be used as proxies among friends in friendly settings, they can be used as trophies, or to show them off in a nice binder. Maybe relive the experience with the English Dub Anime looking cards!?
3. Gameplay utility. Field Center Card and Token ORICAs CAN be used in competitive settings since they simply enhance the experience of the game, similar to any dice or playmats. They have a function that anything can be used for, so why not use an ORICA you like looking at to place on your field?
4. Creative outlet. Aside from buying any of the ones that I myself tried to creatively make, it's a way you can be creative and make your own cards. I can help make them a reality (fulfill the order form to do so). Make your own archetype or just make a single Field Center Card or Token with your favorite anime character on it! Or just put your dog's picture on it. You give me the picture, I can make it.