Salutary neglect happened over three time periods: from 1607-1696, England had no coherent imperial policy; from 1696-1763, England tried to form a coherent policy (navigation acts), but did not enforce it; lastly, from 1763-1775 England began to try and use a coherent policy.
Salutary neglect was a large contributing factor that led to the American Revolutionary War. Since the imperial authority did not assert the power that it had, the colonists were left to govern themselves. These essentially sovereign colonies soon became accustomed to the idea of self-control. The effects of such prolonged isolation eventually resulted in the emergence of a collective identity that considered itself separate from Great Britain.
The turning point from salutary neglect to an attempt to enforce English policies was the Seven Years' War (French and Indian War). Great Britain was fighting France for imperial control of the known world (including North America, where the war was started (see Jumonville affair) and was losing very badly until Secretary of State William Pitt the Elder took charge. To help the war effort, Pitt tried to seize supplies from the colonies, force colonial men into service, and take control of military issues. The colonists strongly resented his interference, and soon Pitt eased his policies.
Nevertheless, the Seven Years' War fostered resentment in the American colonists toward the British and contempt in Britain toward the Americans. These tensions caused England to abandon its policy of salutary neglect, which led directly to the American Revolution.