Open one of the doors on your home. Look at the latch that keeps the door closed. That latch holds the door closed by protruding into a hole in the door frame. Of course that is nothing new, you already knew that. How much force do you think is required to push that little latch through that portion of the door frame? Now, with the door still open, lock the deadbolt. How much further will the dead bolt bar protrude into the door frame? That extra length likely extends past the first board and partially into the second board of the door frame. That distance makes the amount of force required to break open the door significantly higher than when only the doorknob latch is used.
Another benefit of using the dead bolt lock is that you know the door is fully closed and secure. Changes to your home like foundation settling or the swelling of doors & door jams can affect the fit of your doors. Securing the dead bolt lock ensures that the door has closed completely. When you pull the door closed without securing the dead bolt, it is possible that the door did not latch properly and might be opened by the wind, a difference in air pressure or an animal. The end result is that you return home and don’t know how the door was opened or if it was opened by a criminal or even if there is still someone inside. Setting the deadbolt lock will only take a few seconds and is an easy step to help give you peace of mind.