Of course it's useful - all items are useful in some way. xD
The Oval Charm is a Key Item that increases the chances of getting an egg in the day care, when two compatible are in the daycare. You can find one when in Black 2 and White 2 when you catch all Pokemon in the Unova Dex, and talk to Professor Juniper in Nuvema Town. In X and Y, you can find one when you see all Pokemon in the Kalos Pokedex, when you talk to Professor Sycamore in Lumiose City.
Hope I helped. :)
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