The "Girth Hitch" is used in Canyoneering, again as a way to tie a knot to an object. Most of the applications I have seen this used is when canyoneers use a P.A.S (Personal Anchor System) to tie it to their harness.
The reason why you would use this one, is that is is incredible easy to tie and it saves the person from using a carabiner on one side. The other side will need a carabiner so that it can clip into things. Especially when used in "fall protection" scenarios.
This is isn't used for rappelling but rather to attach a rope to an object.
The Girth Hitch is also how you form part of the Prussik knot.
Easy to tie/untie
Easy to memorize
Can be tied with one hand
Canyoneering Usage Examples:
Below, I show you three ways on how to tie the knot, via:
2) GIF (animated picture that repeats itself with no-end)
3) Video (from Canyoneering101 YouTube Channel)