A lot of it depends on your draw length vs the length of your bow.
With my long draw length (33"

, I can't clip my release directly to the string on a bow less than 38" long. The string angle pushes the arrow's nock off the string, arrow hits the ground between my feet. Even with bows over 38", the nock is halfway off the string at full draw and I have to renock the arrow if I have to let down.
With a string loop, the pull is both above and below the nock so the string stays perpindicular to the arrow in the throat of the nock. Arrow stays on the string. I can draw and let down as many times as I want and the nock is still in place on the string.
Plus, the loop allows me to drop down to 32" draw and gives me a few more bows to chose from. Not nearly as many bows are available in 33" draw as there are in 32".