It doesn't require it, but does make the swarm weaker. Some torrent clients allow streaming but it tends to be looked down on by the community.
See here: http://wiki.vuze.com/w/Sequential_downloading_is_bad
173 karma · joined October 12, 2013
See here: http://wiki.vuze.com/w/Sequential_downloading_is_bad
That simply isn't true or realistic for a large amount of people.