What are the advantages of knuckle cracking?

There are none really.

"The common parental advice "cracking your knuckles gives you Arthritis" is not supported by any evidence. A study concluded that there was no increased preponderance of arthritis of the hand in either group; however, habitual knuckle crackers were more likely to have hand swelling and lower grip strength. Habitual knuckle cracking was associated with manual labour, biting of the nails, smoking, and drinking alcohol in the study participants and their families. It was concluded that habitual knuckle cracking results in functional hand impairment and therefore should be discouraged"