Those multipurpose sensors are very versatile! While the obvious uses of it would seem to be for detecting when doors opens or windows open, they do have many other uses! It also has a vibration sensor, orientation sensor, and temperature sensor.
The nice thing about those, is that you can use one to monitor more than one thing at a time. This saves you so much money rather than buying several different sensors for each purpose.
Examples of contact sensors: Opened doors, windows, etc
Examples of vibration detection: Your phone vibration, door knock, laundry dryer completing its cycle
Examples of orientation detection: Garage door, mailbox door
And the great thing about using a multipurpose sensor is that you can use one sensor to monitor several things at the same time. You are not restricted to using one at a time. Example: Cold basement. Have the contact sensor to trigger lights when you enter a laundry room, but that same sensor can be used to monitor basement temperature to toggle heat to warm the basement up!