I needed a separate craft to test my software I'm developing and wanted avoid any risks compared to real multirotor craft. With help of PpmPwm and 1pinDpad library to create RC controller emulator, this emulator can be connected directly into the flight controller. If this would be flyable drone you would have these following risks:

• Danger from propellers (wasting time with removing/attaching them)
   
• My drone is not meant to idle disarmed for hours (some components require some air circulation as cooling)
   
• Requires elaborate setup, drone itself needs a power source, video receiver needs another power source, LCD display needs yet another power source, RC transmitter needs guess what, a power source. And either into hassle and maintain many LiPo batteries. So after experiments you need to go and discharge the residual charge, when you are using it you need be careful not to discharge them too much. If some features require multiple days you need to store LiPo safely because of the explosion hazards. Or you will make extension leads to power all components from single power source, but then you need to modify you RC transmitter to accept AUX power.
   
• If you want to fly next day and you want to work on the firmware day before you need to spend extra time backing up eeprom settings and last stable firmware flash file.
   
• You need a lot of desk space to fit laptop, drone, video reciever, power extension/harness and RC transmitter together on a desk. 

Because non-flyable drone was never meant to fly, some parts which are meant to transfer data wirelessly now can be connected directly (less components and less power sources needed). It's compact on a desk and to store away, it's safe to leave it powered for prolonged periods, even over the night (no risk of LiPos explosions and some components have extra heatsinks which would be too heavy for flyable drone). You can experiment with firmware without worry that it could affect next day flying. No hassle with propellers. It is fast to setup, requires only 1 power jack and 1 ISP connector to flash the device.