In Tree Schema, a data set is a collection of data assets that you choose to group together. Data sets can be used to create orthogonal relationships between your data. Some common use-cases are to:
Group data assets across schemas
Organize similar business-related assets together (e.g. create a data set with all marketing data)
Develop learning plans that users should interact with when they join a team
Link transformations together by tech team ownership
Since you have complete control over how data sets are grouped together you can leverage them to organize your data assets in a way that fits your team!