The decision has a number of benefits. For one thing, it prevents NASA from having to plan an ISS shutdown just six years from now (a shutdown, in this case, means crashing the space station into the South Pacific) and allow them to continue doing important research such as determining how a spider would spin a web in zero gravity.
Senator Bill Nelson of Florida said that the extension would help NASA add jobs at the Kennedy Space Center in Cape Canaveral. The station and its related initiatives currently cost NASA about $3 billion annually. Its stay of execution isn't particularly surprising given the fact that it was only officially completed three years ago.