I recall reading a Douglas article about the chines on the DC10 that stated the reason they were fitted was to prevent spilllage of disturbed airflow off the nosecowl at high angles of attack impacting the leading edge inboard of the pylon affecting lift and increasing landing speeds/distance. Douglas started out with much longer chines that ran over the fan cowl as well as the nosecowl and steadily shortened them until they achieved the desired landing performance with the shortest chines. They were only required on the inboard side but as the nosecowls were not "handed" they were fitted on both sides so the cowl could be used on L or R engines without modification. I think there are some aircraft models around where you do have to remember to relocate the chine to the inboard side if swapping cowls L to R.