-1 : it's not respectful to the people who can't leave because there's not enough people to finish the fate. It happened to me, we were on a boss fate, at 90% most of the team left, and it took us the same time to do 0=>90% as 90=>100% because of that...
If everyone were "efficient" as you say (I'll call it selfish) then no fate would finish, and you're "efficient" way would be "ineffecient" too.