Following a discussion from DABs review of the Bitscope Blade Uno, I thought it was worth quickly mentioning the different sockets and pins you get on the bays of the blade.
This is a standard 2mm x 40 way socket for mounting the Raspberry Pi, it will fit all of the 40pin Pi including the zero.
This a 3 pin header with Gnd, +5v and Gnd. The power is aways on when there is power to the blade.
This is a 2x2 header with a jumper connecting +5v with the Pi sockets for 5v power. You can remove the jumper to disable the socket or attach a switch or relay. The other 2 pins are GND and GP21. This means that you could wire up a shutdown button to all of the Pi to be controlled either from a master controller e.g. the Pi in Bay one or an external switch. It might have been nice if Bitscope had provided a bit more information about what you might do with this connector as per the examples you see for some of the Pi UPSs.
This is a cut-down version of the GPIO header on the pi, it is a right angle male connector on the bottom of the board. There are 26pins broken out including serial, I2C and some GPIO. So you could potentially wire these up to a custom board or across to a Pi accessory board. It does not include the Eprom pins needed for true HATs to work correctly.