The finger ring provides a few benefits. First, a secure draw. By hooking your finger into the ring, you have begun your draw, and by design, the knife becomes married to your skeletal system. Next, it allows an increase in grip security. Because of the way it is held, the kerambit becomes very hard to dislodge or disarm while the finger is through the ring. And finally, as with other ringed or holed blades, the ring on a kerambit allow you to keep the knife secure in your hand, while using that same hand to perform other tasks. And then, a quick twirl or spin, close your hand, and the knife is ready for more work.
The final aspect of the finger ring is its use on the kerambit as a fighting weapon. By securing the knife to your hand using the ring, it increases the force with which you can safely cut and thrust with the kerambit, especially on pull cut motions. This is where its likeness to a claw really becomes noticeable.