Originally Posted by
RonH
If the limit screws are adjusted correctly and you don't ever screw with them (no pun intended), then the dd isn't needed.
That's it. The limit screws keep the chain from going too far. Now if you ride a bike without proper maintenance (chain gets gunked up, no lube, stretched, cables not adjusted, etc.), it's maybe a concern. IHaving one doesn't really distract from the bikes performance that much but it does send the message that the rider doesn't do a lot of maintenance.