Primarily it's highly sensitive due to the possible contrast: in absorption spectroscopy, you usually have the ingoing light and your peaks often are just small features on a huge background. In fluorescence, you don't have to deal with that, you can set up a suitable geometry so that your ingoing light isn't even seen by the detector which means you can detect small features which would be invisible in absorption.
Selectivity can be enhanced by making maps of excitation vs. luminescence wavelengths which means you have two potential characterization markers and not only one as in absorption.