Group work is a valuable learning device that teaches teamwork skills which students will use no matter what profession they enter. It is perhaps even more valuable in online classes, as more and more organizations are using distributed employees who need to coordinate their work from a distance.
But group work also brings with it the danger of social loafing, those one or two students who do not contribute their fair share to the project. Not only does it undermine the quality of the project, but it creates frustration among other group members who see it as unfair to have team members not pull their own weight. This can have a dampening effect on the motivation and thus performance of other members of the group.