Scrotal weights, most commonly in the form of split-steel stretchers, usually serve a number of purposes. First, they can be used for scrotal stretching; that is, to lengthen the scrotum. That said, not all ball weights will stretch the scrotum, and there are also many alternative methods. Second, many find the weights aesthetically pleasing, and many also enjoy the feeling of wearing the weights.
Most weights encircle but do not fully encapsulate the scrotum. Those that do are usually called ball crushers.