This feature terminates all existing TCP sockets that exist on your system at the moment of the VPN being connected.
Some software maintains persistent connections to IPs. When the VPN connects, those sockets can remain open, and continue to transfer data, bypassing the VPN tunnel entirely until they get closed and re-created. This can leak data using your ISP assigned IP even when a VPN is connected. This unique Windscribe feature prevents this from happening.