Designing GSS that can be used effectively by co-located groups presents a number of specific problems that do not exist with other group configurations. In particular, any GSS in a co-located setting has an overhead of use that must be recouped by its benefits, or it reduces the overall group effectiveness. In distributed groups the same basic payback is necessary, but usually the GSS is also used as a communication medium; in co-located groups, members communicate directly so this immediate payback is not available to them and the benefit must come from the decision support strand of GSS.