Different laws have different interpretations, case precedents, and rules for who has standing to sue under them. By reversing, and permitting suits under both laws, SCOTUS has given victims of sexual harassment more opportunity to make their case in court. In addition, the laws in question here have different remedies available and including Section 1983 means that individuals may be sued as well as official entities.
Of course "making a case in court" is not a guarantee of a win, but it's a definite step in the right direction.
(Oh, and they refused cert for Mukasey v ACLU, which pretty well means that COPA is dead. Yay for that, too!)