Studies in the Planning Support Systems (PSS) debate are increasingly paying attention to the support function of PSS. This involves among other things studying the usefulness of PSS to practitioners. This paper adds another dimension to this evolving debate by arguing that planning tasks should receive more attention. Although planning tasks are central in several PSS definitions, they have hardly received explicit attention in empirical studies. In an aim to fill this void we conducted an empirical study based on the perspective of tasktechnology fit. The latter consists of a combination ('fit') of analytical and communicative support capabilities ('technologies'), and three types of planning tasks: exploration, selection and negotiation. Next, we selected four case studies in the Netherlands, in which the same PSS was applied, which consists of a combination of the CommunityViz software and a touch-enabled MapTable. The cases differed in the planning tasks that were central during the workshop, resulting in different kinds of usefulness attributed to the PSS. For instance, in one case with a selection task the communicative support capabilities contributed to the transparency of the process, whereas in another the analytic support capabilities of the PSS improved the task of negotiation because of the iterative feedback it provided. The paper concludes with the observation that the concept of task-technology fit has potential be applied in different contexts and with different types of PSS.