Some team members are not motivated to perform well under these circumstances. In the real world a marginal team player has a . . . In a group of students this does not occur. It's very difficult to motivate some students. There is too, the problem of differing standards.
Some students are happy just to pass a course, while others strive for A's.
Resolving conflicts between different performance standards is a problem. My experience in working within groups has been that self-selected groups work best. Assigning these intermediate tasks gives us a solid timeline to work with. It is better, because I concentrate the problem very much to be clear understand it. It's help not only understand on scientific, but also on performance.