The Benoni Defense is an opening for the ultimate street fighter. It's a voluntary sacrifice of central space. You're creating a cramped position for yourself. White will try to overwhelm you in the center. He will do this by playing against your main structural weakness, d6.
No one would do this if there wasn't some compensation involved. Here the pay off is claimed by playing in classic hypermodern fashion. Trade off a piece, usually your light square Bishop, to alleviate the space problem. Then attack White's center from both wings.
You've got your powerful dark square bishop on the long diagonal. You need to get your Knights on to good outposts. Sometimes it's e5 and h5. Your Queenside Knight can in other lines find himself slipping into c5 after the ...c4 advance, ready to plant himself into d3. Black must play aggressively and material sacrifices and imbalances ought to be regarded as standard procedure for the regular Benoni player. This is a sharp opening with chances for both sides.