They will not prevent all injuries, but protect in normal work circumstances where injuries can occur that could make you lose the use of the hand.

Things that you must protect if you are in a survival situation:

Eyes

Feet

Hands

Even if the injury is not life threatening in itself, if it limits your ability to perform the functions necessary for survival, it becomes a life threatening injury. Even if you wear contacts, you might seriously consider carrying glasses as a back-up for their protective qualities.