Never known them as rim locks - first thing I thought of was the one on my bathroom door ....
Security bolts is what I've always known them as and, as KiwiGF says, used on trial bikes when running at ultra-low pressures to prevent tyre slippage on the rim. Another device we used in sand racing was a special tyre where the valve came out the side of the tyre instead of the rim so, if the tyre slipped, the valve wouldn't be pulled out. Serves no purpose on a road bike except to unbalance the wheel.