Why is it useful to have a magent that can be turned on and off?

A magnet that can be turned on and off, known as an electromagnet, is useful because it allows for precise control over magnetic fields. This capability enables applications such as magnetic levitation, where objects can be suspended in mid-air, and in electric motors, where the magnetic field can be adjusted for different speeds and torque. Additionally, electromagnets are essential in devices like magnetic resonance imaging (MRI) machines, where the ability to switch the magnet on and off is crucial for imaging processes.