Basically being able to have 2 armor exotics at the same time or 2 exotic weapons at the same time. Think of the possibilities. Personally as a titan, i would love to have Khepri's Horn and Alpha Lupi. Or.. Huckleberry and Fighting lion. (damage field of enemies with Fighting Lion, switch to huckleberry, mow them down, instantly get ammo back on both, no reloading, ever.)