I see it's been a while since yourfirst asked your question, so I may be wasting my time posting.  NSA is practiced around the world but is seen most often in the U.S. primarily because its founder, Dr. Donald Epstein, first began training DCs around the NY area.  The name "network" is significant here because Donald took concepts from many other different techniques and incorporated it into a specific analysis and treatment system in which he named NSA.  To keep it simple, Network focuses mainly on structures called the meninges.  The meninges consist of 3 layers and they surround the brain and spinal cord.  It is theorized that the meninges can hold emotional garbage and that by releasing this, it frees up the spinal cord allowing for proper flow of information.  It therefore allows the innate wisdom of the body to run more efficiently.  It is administered by the D.C. applying very light pressure to certain points along the spine, occiput and pelvic regions.  In the past, more adjusting (what you referred to as "cracking") was performed.  Over the years it became less and less.  Most practioners will only adjust when they feel the spine "tells" them to do so, or when they feel the spine is ready for the adjustment.  Some people notice changes instantly, some after a while and some none at all.  There is a potential to have a "release" on the table....meaning an emotional release.  It's not effective on everyone, but for those individuals, another form of energy work may be more appropriate.  Hope that helped a bit!  :)