Port security is a useful feature as it protects against too many MAC addresses per ports and can dictate which MAC address is allowed to connecte against which port. However, if the hacker knows which MAC address is permitted on that port, he will gain access to the network by spoofing the MAC address. Port security also prevents unauthorized extension of the LAN in case a user decides to attach a hub to connect additional hosts. You have to allow only a single MAC address on the secure port to prevent this sort of extension. Also, if you are concerned about spoofed MAC addresses to bypass port security, then consider implementing IEEE 802.1X authentication mechanism.