Strike plates reinforce residential doors by adding stability to the door jamb, making it more difficult for someone to force open a locked door by damaging the jamb with the door's bolt. This is particularly true when the strike plate is constructed from more durable materials than the door jamb. In this case, the strike plate both fortifies and supports the integrity of the door jamb.
Strike plates also supply door jambs with protection against the friction of the regularly extracting and retracting bolt. The hole in the strike plate lies over the hole in the door jamb where the bolt extends into, thereby also helping to keep the bolt in place. Sometimes within the strike plate's hole is a spring or bar that extends into a hole in the bolt itself. This spring or bar helps to ensure the bolt does not move unless turned with its appropriate key.
Strike plates are often used in conjunction with face plates to help protect doors and door jambs from splintering when someone tries to break into a room using exorbitant force. The face plate sits directly on the lockset and, similar to the strike plate, reduces friction and reinforces the materials of the door and door jamb.