Use of Cracker
The characteristic whip-crack sound that a sling can make when slinging is largely due to the use of a cracker or integrated tassel at the end of the release cord. The cracking sound has no direct effect on the shot itself, it won’t make the shot more powerful. However, apart from the fun of a cracking sound, there is also some great utility that comes with cracking a sling.
When form and effort harmonize you will be rewarded with a solid crack of the sling. Crackers give you immediate feedback on the quality of your shot and will help you identify a needed adjustment or reinforce that what you are doing is correct. When technique is out of whack you will know it through a weak crack or almost no crack at all. Also, if the cracker "bites" you as it passes through your hand then something is off about technique. The release should be clean and you should not feel the cracker.
Keep in mind that slinging accuracy is somewhat independent of throwing efficiency. But when you get a solid crack you will hear and feel that you have gotten the most efficiency and power out of your effort. Similar to how your best outcomes in other sports are the ones that feel almost effortless, everything just lines up.
Also, the use of a replaceable cracker is a great way to preserve the end of your release cord. There is a tremendous amount of speed at the end of the release cord as it uncurls and snaps. The energy released can deteriorate this section of the sling quite quickly, often more quickly than rock abrasion in the pouch/cord abrasion area. We call it whip-crack fatigue and we make a great sling wax to fight it. But the cracker can also act as an energy sink to help absorb some of this force rather than all the force released at the end of the sling. It is similar to how a cracker helps preserve the fall of a bullwhip.
A detachable cracker is also convenient when you want to remove it for a less conspicuous slinging session. A cracker is like giving a sling a megaphone. Cracker or not, slinging catches the attention of people passing by and they often stop to watch. We have found that various expletives go hand in hand with curious observers who see a sling in action for the first time.