In short, it means that the places where extraterrestrial life might be found could be far more numerous than was previously believed.
Prior to this discovery, it was believed that there was only one combination of elements that could result in life, and that certain elements, such as arsenic, were toxic to life.
In terms of astrobiology, this meant the search for extraterrestrial life was limited to looking only for those specific elements, and only for "safe" environments on other planets. NASA's announcement means that the search can be expanded to look at other chemistries and environments.
If life can be made from two combination of elements, are there other valid combinations elsewhere in the universe? If life can exist in poisonous arsenic, and even use it in its DNA, what other environments could it survive in?