The D-ring is made of sturdy 8mm thick aluminum and in tests the breaking strength has exeeded 400kg which means that you can use it for lots of different purposes, for example to hang up the equipment, pull an animal or anchor a dog leash to your waist. It can also be used for suspending a tarp or hammocks.
Note that the D-ring should not be used for climbing since a bad fall can create forces that exceed 400kg even if the person is not heavy.