I generally like 3rd place matches, particularly the World Cup. If the coaches put in fresh players or those who didn't play much prior in the tournament, then they can often be entertaining open matches. Also sometimes a 3rd place games can provide some interesting matchups.
The problem with the Confederations Cup is that they are only 8 teams with only 2-3 legit contenders. . So the 3rd place match doesn't seem all that necessary, especially because often the teams already met in group play.
But I think the 3rd place match is fine in the World Cup or any major tournament where there is 16+ teams.