"Discharge and charge rates are often different for li-ion cells. A separate port implements current monitoring just for charging and another one for discharging.
When current exceeds a threshold it will activate the safety disconnect."
https://www.reddit.com/r/18650masterrace/comments/hyuakp/common_port_or_separate_port_on_ebike_bms/
I'm going with a common port BMS on my ebike just because I'm using a hobby rc charger and it can monitor the charge cycle and alert me to any issues. So I wont need a separate port.
Heres another good thread on the topic.
https://diysolarforum.com/threads/bms-common-port-vs-seperate-port.468/