For HADS star or Exoplanet transit work, often a classic R-filter is recommended for more stable background.
When working with BVRI filterset, I run into the problem that APASS seems difficult to use as reference, because it only has classic (Johnson-Cousins) B,V bands and Sloan u’g’r’i’z’.
So when using a classic R-filter (Cousins-Bessel?), you always need color transforms to use APASS. Does it make sense to use a single extra Sloan r’ (red) filter, because that seems a fairly simple linear transform to Cousins R. Also for Gaia DR3 you have well documented higher order color transforms to BVRI.
So bottom line, starting with BVRI filters, would a SLOAN r’ filter help to get a better Cousins R-calibration, because APASS doesn’t have the R-band ?