Flow control support is limited unless all equipment can use it. If a 10 GbE host and 1 GbE host are connected to a switch, the one host can overwhelm the other.
Assuming flow control is not supported. In general, how does the switch control sending too fast or does it not do anything to control it? Is it left to the protocol layer, such as TCP having its own flow control algorithms as compared to UDP having no flow control?