Folding knife have excellent portability and safety, but they also have structural weaknesses. The first is the strength and durability of the poor, followed by from the storage to the state can be used, to spend a certain amount of time.
When the folding knife is pulled out of the sheath, the blade must be opened, so that it adds an action to the scabbard knife, and the momentary delay will be the life-and-death diver's knife and the mountaineering knife, which is the reason why all the scabbard knives are used.
Even if there is no such a serious situation, it is very inconvenient for the operation to be carried out with both hands. It would be nice if you could do it in one hand.