We calculate spectral models of advection-dominated accretion flows, taking into account the possibility that significant mass may be lost to a wind. We apply the models to the soft X-ray transient V404 Cyg in quiescence and the Galactic center source Sgr A*. We show that there are qualitative degeneracies between the mass loss rate in the wind and parameters characterizing the microphysics of the accretion flow; of particular importance is delta , the fraction of the turbulent energy which heats the electrons. For small delta , current observations of soft X-ray transients and Sgr A* suggest that at least ~ 10 % of the mass originating at large radii must reach the central object. For large delta ~ 0.3, however, models with significantly more mass loss are in agreement with the observations. We also discuss constraints on advection-dominated accretion flow models imposed by recent radio observations of NGC 4649 and other nearby elliptical galaxies. We conclude by highlighting future observations which may clarify the importance of mass loss in sub-Eddington accretion flows. \noindent Subject headings: accretion, accretion disks - black hole physics