Hi Guys,
Perhaps I can add clear up some confusion regarding the "butterfly stretching". Before I answer let me give my qualifications on the subject.
I am a professional Yoga instructor that works in the fitness industry. I work with pro level atheltes and many people with injuries on a regular basis.
The stretch you guys are describing can be a good one, when done correctly. Never bounce stretch. It tears up your body and leaves you prone to injury.
The "butterfly" does not damage connective tissue.(unless done in a bounce stretch manner) It stretched deep hip flexors, knees, lower abs and relaxes all the internal organs in the abdomen.
Word of caution, people with knees issues or herniations should not do this exercise until those restritions are healed.
In Hatha Yoga this stretch (called the gentle pose) is an intermediate posture. Takes years to reach it. Most people also try to do before they are properly warmed up. If you do attempt, go slow and most importantly breath.
Hope this helps,
Brian
San Francisco, CA