Electrical Connectors - To Split Pin or Not To Split Pin, That is The Question
From Tyco Electronics Soft Shell Pin and Socket Connectors, page 173.


  "Notes:
  1. Split pins recommended for use in housings having 6, 9, 12 and 15 circuits to reduce mating force."


If you look at the TE document 110-213, page 3 under Mating force, you can see that the split pin has less than 1/3 the mating force than the solid pin.