It comes in handy when you need to program a bunch of STM32F103C8T6s. (Note: I made a similar ‘cradle’ for programming bunches of ESP8266s’. Read about that here.)
A standard USB to serial converter is attached to the 6 pin header shown on the right side. Here are some pictures. When the STM32F103C8T6 is ‘plugged in’:
This Fritzing graphic shows how the connections are made from the USB to serial converter to the STM32F103C8T6:
Download the Fritzing source here.