Great read from the CrossFit Archives, must do this lift properly every single time!
The deadlift is unrivaled in its simplicity and impact while unique in its capacity for increasing head to toe strength. Regardless of whether your fitness goals are to “rev up” your metabolism, increase strength or lean body mass, decrease body fat, rehabilitate your back, improve athletic performance, or maintain functional independence as a senior, the deadlift is a marked shortcut to that end. The deadlift’s primal functionality, whole-body nature, and mechanical advantage with large loads suggest its strong neuroendocrine impact, and for most athletes the deadlift delivers such a quick boost in general strength and sense of power that its benefits are easily understood. If you want to get stronger, improve your deadlift.” http://library.crossfit.com/free/pdf/12_03_Deadlift.pdf