It is critical to clean both ends of the connector pair to get optimal network performance. Contamination that is not removed will cause unnecessary signal loss (and that's the best case scenario) and can even cause permanent damage the surface of both connector end faces (pretty much worst case). The industry standards — IEC 61300-3-35, IPC 8497-1, and IEC 62627-01 — all are unanimous and insist on the same process for visually inspection and cleaning both connector end faces before mating.
Cleaning fiber end-faces ensures a reliable network
Check out the white papers and videos on this site about cleaning your end-faces. Your fiber will thank you!