Participation in data-driven projects is a popular approach and often connected to the idea of more equitable projects. The lack, however, of an agreed definition of what constitutes participation leads to fuzziness surrounding possible motivations for participation. This in turn diminishes the ability of facilitators to communicate what to expect from a participatory process to participants and the public. To better understand this, we conduct a systematic literature review and analyse the claimed motivations for implementing participation in data-driven projects. We find three overarching categories: value-, effectiveness-, and efficiency-focused motivations. We discuss overlaps and issues within these categories, such as the implications of project-internal demands (the realisation and working of a project) and project-external demands (codified demands in frameworks, policies and rights).