Not sure this is universal but in my field of interest (steam turbines), we are interested in saturated steam because that is what we get in the last stages of the low pressure turbines. In our case, moisture is detrimental to the performance of the turbine, so it is important to be able to predict the moisture content aka liquid fraction aka (1-steam quality).
Saturated steam tables at thermodynamic equilibrium are one way to get this information.
Now, we could be (and are) interested in steam in a subcooled state, i.e. steam that remains dry at temperatures lower than the saturation temperature. This state is in fact often encountered in steam turbines, because the flow is expanded so fast that steam "doesn't have time" to condense at equilibrium. It remains dry, until the temperature/pressure conditions reach a threshold called the Wilson line. Then, condensation happens and thermodynamic equilibrium is restored.
The properties of subcooled steam are usually extrapolated from the properties of superheated steam.
Whether you are interested in saturated steam at equilibrium, or subcooled steam, the reference data for the industry is the one from the International Association for the Properties of Water and Steam (http://www.iapws.org/relguide/IF97-Rev.html)