They are directly related to the needs of the individual. They are less risky. There is high level of commitment and motivation in individual projects. There are less legal implications and difficulties. More risks due to divergence among members.
Some members lack commitment.
Selfishness of some members who want to get more from the project compared to what they put in it. This can result in meagre output because actual contribution is only from a few people. Lack of legal contract among group members can create problems. Newly formed groups do not understand what it means to work as a group and to take collective decisions. Some groups start projects which are not related to their physical and mental abilities.