This is definitly a widely known and practised technique, especially among hobby artists. The amount of realism possible with this technique is definitly a lesser known fact. Most often this
technique is used quite onedimensional as a simple wet in wet technique of colors flowing together on a wetted paper. A more complex variation of glazing and wet in wet painting, always controlling
the flow of water leads to more work and achieves more realism. Since 2002 I started using chinese white to give some areas of the painting more "body", which definitely opened my range of sujets in
watercolour painting. As a technique this was used widely at the time of the victorian watercolor masters.
Another variation is the use of acrylic sepia ink as an underpainting (e.g. Tuscany roofs).