Impact of emission lines in the input spectrum on inferred galaxy properties. The upper panel presents the difference in the fitted M_★ between attSN_Z_SNE (which excludes emission lines from the input spectra, but includes them in the fitting) and attSNE_Z. Emission lines have the strongest effect in low-mass galaxies. The reduction in fitted M_★ arises because attSN_Z_SNE infers younger stellar populations, producing a bluer continuum to match the observed colour in the absence of emission lines. The lower panel illustrates this change in stellar populations by illustrating the distribution of differences in mass-weighted age between attSN_Z_SNE and attSNE_Z with the median marked by a dashed line.