For a feeling of cleanliness and freshness. Particularly after sex, the vagina can smell rather ripe if left uncleaned internally. However, physicians caution against douching as it destroys the vagina's natural pH factor.
Women douche for the sake of cleanliness, internally, within their vaginal walls, usually after their period or perhaps after a pattern of unprotected intercourse to remove sperm and egg debris.
Women douche because they're too lazy or busy to bathe or shower. Me personally, I think its disgusting and would prefer a hot bath over a wet nap. But the concept, is found to be very convient