It allows a group of users (or peers) that are collaborating to share a given file to do so more swiftly and efficiently.
By reducing dependency on a centralized tracker, PEX increases the speed, efficiency, and robustness of the BitTorrent protocol.
In the original BitTorrent design, peers then depended on this central tracker to find each other and maintain the swarm.
To make initial contact with a swarm, each peer must either connect to a tracker using a ".torrent" file, or else use a router computer called a bootstrap node to find a distributed hash table (DHT) which describes a swarm's list of peers.
[4] To create a PEX protocol providing a uniformly-distributed peer selection, one could form a small distributed hash table (DHT) local to a torrent.