socket MSG_DONTROUTE option on local sockets

Hello, If i use the MSG_DONTROUTE option on a local socket, i mean a tcp socket (AF_INET or AF_INET6) with this option. I know that first of all using the tcp AF_INET or INET6 is a dumb decision instead of using the AF_UNIX family, but i have come to a point where i couldn't change this as this code is legacy. If i use the MSG_DONTROUTE option will that be a performance gain on the sockets that communicate inside the system, not to outside? I am guesssing that routing lookup performs once and then it will never. for every packet there is no routing lookup performed so there wont' be much gain in performance? thanks,