It allows for multicast and broadcast operations in which the same data are transmitted to several recipients in a single transmission.
In connectionless transmissions the service provider usually cannot guarantee that there will be no loss, error insertion, misdelivery, duplication, or out-of-sequence delivery of the packet.
In connectionless mode, there is less opportunity for optimization when sending several data units between the same two peers.
By establishing a connection at the beginning of such a data exchange the components (routers, bridges) along the network path would be able to pre-compute (and hence cache) routing-related information, avoiding re-computation for every packet.
In connection-oriented communication, network components can also reserve capacity for the transfer of the subsequent data units of a video download, for example.