neither is to get a proper shot of a target ...
Indeed, but in that case you get, with some practice, a good indicator of the quality. You can generally see on the matrix result if the shot suffers from large measurement errors, huge lightness errors along the neutral axis especially on the black patch, or over-saturation = glare. With a badly measured SSF the profiler still sees a "perfect camera" (but the wrong camera) so you get no indication of measurement error in the matrix or LUT calculations, you just have your eyes to decide if the final rendered image seems to produce sane result.
Target measurement errors usually leads to some saturation errors, hues are still correct. Lightness is generally not compensated for, unless you do reproduction, so the typical workflow is very robust against that. As cameras make a pretty good matrix-only match these days, the result gravitate to something linear and sane in the relax stage, further enhancing robustness.
SSF measurement errors however, I think has a tendency to also produce hue matching errors (which I think is a worse problem), but maybe I'm wrong? Although I have made many theoretical experiments with SSF I actually don't have the experience from making SSF measurements, so I stay humble about the subject.
