One place where brown dwarf (BD) and exoplanet science overlap is atmospheric characterization by spectral methods. If you get reasonably well-resolved spectra

One place where brown dwarf (BD) and exoplanet science overlap is atmospheric characterization by spectral methods. If you get reasonably well-resolved spectra from the BD, you can invert to obtain information about its atmosphere's composition and density/temperature profile. The BD is going to be more emissive than an exoplanet (and a BD has no light contamination from a nearby host star) so the BD is not an exact analog, but BDs provide a workshop for development of inversion approaches. [e.g.: https://arxiv.org/pdf/1410.6512.pdf https://arxiv.org/pdf/1410.6512.pdf]