It's nice to set up the lowering system so ropes don't rub on the tree, the clock hitch allows freedom to slide the porty right into the best spot, and move it as needed throughout the job. Not a big deal. A clock hitch is tied similarly to a timber hitch except the porty is attached to two lines making it stronger.
If it takes the same time to tie, it's stronger, and can be moved easier, why tie an inferior not?
The whoopie slings are a PITA. I consider them an option to learning to tie a good knot. If I was going to use an adjustable sling, I go with the loopie.