As far as I can tell it’s basically vertex paint, but in sculpt mode. It allows you to sculpt and paint without changing modes.
Also with some added features, though I suspect the features should be available in both modes.
A good tutorial: https://www.youtube.com/watch?v=u-FpZFe2OzI
One of the coolest things in that tutorial is using the output of a high poly model and applying it to a low poly model.
