When you model a solid (non sheetmetal) part and use the shell tool to hollow it out you can convert the part to sheetmetal. With a convert tool you can convert all the edges to rips and with some innovative use of those rips design the part to unfold a specific way. With the rip tool you can simply split one wall in half so the unfold works like you want.
Rip is an option in the create bend feature. It is under relief. Basically when you bend a part it gets loaded with stress. Rip pretty much allows it to crack at the end of the bend line.