Its easy to change your camera lens but its even easier to get dust on your sensor. This best practice will help you prevent getting dust and debris on your camera sensor as well as prevent potential damage to the mirror or sensor.
Products seen in this video:
Canon EOS 5D Mk.III
Canon EF 70-200mm f/2.8L Telephoto
Sony a7 II
Sony FE 70-200mm F4 lens