Hello,
All flow control arrangements for the MCU end will need to be specifically written, to take into account your chosen size of receive buffer. At the PC end, assuming you are using some sort of terminal program to provide the communications, flow control will happen, if it is enabled. Unless you are sending or receiving data strings that can exceed the receive buffer size at either end, flow control won't normally occur, even if enabled at the PC end.
For interactive communications, with manually entered commands, where the MCU would generate a response to each command, it is unlikely that flow control would ever be needed. In this case, the MCU receive buffer would be of sufficient size to hold the command line data, and command processing would commence on completion of the command entry. In this case, it is likely you would want to "echo" each character as it is received.
Regards,
Mac