With the calibration markings on the VPI arm it makes it really easy to reset the VTA for different weight records. 120, 180 and 200g LPs are all different thicknesses. But once you set the correct VTA for each one you can not the numerical setting on the VTA knob and switch it back and forth for the different records.
Getting VTA close is nice, but getting it dead on perfect is way better and the on the fly kob on the VPI allows tou to have it perfect for each record, not jsut for one particular one.