It has been practiced since late last century when Louis Comfort Tiffany and John La Farge did a lot of plating. Stained glass plating looks great when viewed from the front, but pretty awful when viewed from the back. This is because most plating occurs on the back surface of the panel. It gives a sense of distance to the piece. To get this effect of distance the layer closest to the viewer should be a dense, thick opal glass.
Dense glass diffuses the light passing through the layers and gives the desired diffused look.
Many Tiffany panels feature this effect. To add shading to a piece. You need a relatively dense glass, otherwise the line will be too pronounced. To modify glass colors and textures. By plating glass together you are not restricted by the color or texture selection available at the retail store.