Please explain why is saline used for wound cleansing?

Basic and gentle: Saline is basically a weak solution of salt in water. This closely matches the basic fluid component in our bodies and therefore is very similar to what the cells are used to "bathing" in. Things like betadine, peroxide and alcohol are very damaging to the cells as is "letting the air get to it". You should wet a gauze pad with saline and gently clean the surface of the wound. Dress it after.