Earth connection on plastic back box

I have replaced an external socket in the garden and I noticed that the back box has an earth connection, like shown in the photo below.

This is also on the old back box but it was never connected.

I saw a youtube video and the guy says that this connector on the back of the box is to stop the switch being pulled off the back box as the earth cable runs from the switch to this back box.

Is this its purpose and do I need to connect this second earth as it wasn't connected before.