You can do more type of imaging aside of shooting through RGB filters. Sun in white light (Baader astrosolar) is shot through a narrowband filter like solar continuum. Solar H-alpha is also narrow. Moon is very ofthen shot with infrared filters. Those cases would be bad for color cameras as only some pixels would be used.
For planetary imaging you can shoot RGB channels one after another. It's more work than color camera, but like it allows you to refocus each channel or set different settings. Low altitude targets like Saturn will focus at different points for different wavelengths - so mono camera may limit atmospheric dispersion by refocusing. Also mono camera can shoot planetary luminance channels - in infrared or infrared + some visible light. Venus can be also shot in UV band, Jupiter in methane band.
:)
