First and most importantly, through his love of Orientalia of all sorts he introduced a new manner of dressing that released women from the spine curving, waist crushing corsets that had been the mode. Suddenly the waist returned to a level unseen since the 1810s. And clothes fell in loose folds, with no restrictions in the midsection. Of course corsets didn't actually disappear, but they changed radically, to a shape much closer to a human norm; and many women did in fact go without entirely.
He also engaged the services, and encouraged the careers of young artists, like Georges Lepape (whose illustration of Poiret's work is below), and Paul Iribe; both of whom drew fashion illustrations for expensive, and exclusive folios of current design work from the house. This began a collaboration with artists and photographers that is an intrinsic part of how fashion works today.
He was also a master showman, and created lavish parties which became much talked of and recorded; which only furthered his fame and influence. The most extraordinary of these was the 1002nd Night party, held in the gardens of his home. All the guests were costumed by him, and this photograph is of the costume he himself wore, along with that worn by his wife and chief muse Denise. No expense was deemed too much, including covering the garden paths in carpets, having caged birds and monkeys, and peacocks roaming about.
But for me, it will always be his remarkable critical eye, that never made something lavish simply for its own sake. Everything was integral, and if it didn't contribute actively to the harmony of the design, it was rejected. Drama was fine, and in fact, actively sought, but rococo abundance was not.