Originally Posted by
HillRider
External cam skewers can't develop as much clamping force as internal cam skewers. For vertical rear dropouts and rim brake forks, that's not an issue as their clamping force is adequate. The problems arise in frames with horizontal dropouts or disc brake forks where their clamping force can be inadequate to keep the rear wheel positioned properly or keep the front wheel retained in the dropouts. The later then depends on the "lawyer's lips" for wheel retention.
I believe it's more correct to say that external cam skewers require more force to close in order to achieve the same clamping power as an internal cam skewer, but if you're not strength limited, either type of skewer can provide adequate clamping force.
As an aside question.. is there such a thing as using too much clamping force?