When to Double Up

doubleupI spent my teacher workday at a MathForward workshop. The presenter used a SMARTboard and an additional LCD projector onto the board. Seemed like an exhaustion of technology; however this was a logical a solution if you need to write on that worksheet that is projected by your document camera OR do not want two surface images to interact (Also this allows the user to break away from that goofy SB transparent layer).