Some quick thoughts…
A context view in a smart folder can be mirrored or not. In the former case, then yes, it behaves a lot like a relation view.
A non-mirrored smart folder context view is an entity-specific view, whereas mirrored views and relation views are database-specific.
Typically, relation views are used to simply show the linked entities for the field they belong to (although see this) whereas smart folder context views might be more appropriate for complex views which involve multiple types.
Smart folders and their views are also useful as left menu navigation points, and can be turned into smart sections, which allows you to better achieve a ‘matrix’ organisation of data, e.g. spaces can represent departments (sort of grouping by roles) and smart sections can represent projects (cross-functional information).