LEED v4 takes everything that was successful about LEED 2009 and streamlines it to create a more flexible user experience. One of the ways USGBC has done that is to develop a new set of impact categories that align more thoroughly with the vision of LEED.
The LEED impact categories outline the market transformation that the technical requirements then work to achieve and help determine where points should be assigned. The categories focus on the social, environmental and economic goals of LEED and that measure each strategy according to its ability to meet those goals. Rather than focusing on environmental problems and how they can be reduced, as LEED 2009 did, the LEED v4 system asks, “What should a LEED project accomplish?”
For more background, take a look at our process overview for impact categories. It explains the evolution of LEED credits and what's involved in point allocations. In addition, you can take a look at Appendix A for a description of the goals behind each impact category.