It is critical for intuition and awareness. People with highly developed pineal glands can be psychic.
http://www.scribd.com/doc/4286031/Aw...-The-Third-Eye
What suppresses it can be debated. Did God turn it off after the tower of Babel? Is it just unused in humankind? Is it part of the puzzle of life that each individual needs to find for themselves? Nobody knows for sure.