While the court did not reach an actual conclusion on whether or not there was cohabitation by the ex-spouse who was receiving support, the Landau case was important.
Before Landau, an ex-spouse who was paying support could make an allegation of cohabitation and be permitted costly and invasive discovery ordered by a court. The Landau case required that some evidence be produced that there was cohabitation before a court would order discovery.
Before Landau, the ex spouse with more financial resources may have taken a calculated risk with a cohabitation motion to coerce the other spouse into a settlement. A cohabitation trial can be an expensive endeavor for both sides. It forced some supported spouses to engage in settlement discussions when the proofs of cohabitation were pretty weak.
Now, many attorneys use private investigators more for the initial background checks to determine whether cohabitation appears to exist.