Five years after the first direct detection of gravitational waves, over 50 compact binary mergers have been discovered in the data of the LIGO and Virgo detectors. The masses and spins of these compact objects can be used to tackle multiple problems in physics, astrophysics and cosmology. In this talk I will first discuss what can be learned about the properties of the individual gravitational-wave sources, and how the results depend on some of the analysis details, such as Bayesian priors and noise treatment. I will then discuss what can be learned from the overall set of detections. As an example, I will report on recent constraints on the existence of ultralight scalar bosons obtained using the latest LIGO/Virgo data release.