The labia are rich in nerve endings, and in fact so called 'hypertrophic' labia have 50% more of these nerve endings*. This means their owner may get special pleasure from their nibbling, tugging, stroking or licking.
Many men also find that larger labia provide extra stimulation during intercourse, as they rub or wrap around him. For this reason - and those above - many women in Africa (and in the West) practice a gentle stretching technique to lengthen their labia.
In their closed peg-like form the labia minora help to direct the urine stream (useful for hikers!)