Can only use for a few galaxies. Need other methods to estimate distances to very large cosmic distances. Seek new Luminosity Distance Indicators. Must work towards large distances. Each step calibrates the next step.
Errors made in early steps affect all following steps.
Orbits of planets give the geometry. Measure stellar parallax angles Use Earth as the baseline. Relate spectral type to luminosity in calibrated H-R Diagrams. Works OK for individual stars. Distances to nearby galaxies.