Knuckle popping is when you stretch or bend your fingers. The bone of the joint are forced apart. As they move apart, the tissue that surrounds the joint stretched. This increase the volume of space between tissues. With an increase in volume the pressure in the synovial fluids drops forming bubbles. When the joint is stretched far enough the pressure drops so low that these bubbles burst, producing a popping sound. It takes half and half for the gas to dissolve back into the synovial fluids. Once gas is dissolved it is possible to pop knuckles again. Synovial fluid present in your joint acts as a lubricant. The fluid contains the gases oxygen, nitrogen and carbon dioxide.
Habitual cracking just for the heck of it is bad for this joints that are being cracked. Although researcher has not come up with any evidence to show relation between knuckles cracking habit and getting arthritis frequent and habitual cracking may lead to joint swelling. Also studies have proven that habitual knuckle cracking over years as result of knuckle cracking addiction does lead to decrease in the grip strength.
Cracking your knuckles after a long period of monotonous long activity helps loosen the joint and relieve knuckle pain and stiffness. The joints no longer feel rigid and inflexible. This is because muscle around the joint feels relaxed after popping them. But cracking knuckles to often may cause damage to your soft tissue and surrounding ligaments.
Scientific American. (2012, May 6). What makes sound when crack or knuckles? Retrieved from http://www.scientificamerican.com