If you want to allow API consumers to request resources hierarchically, i.e. filter by relationship, expose them as sub-collections of the main collection entry point.
E.g.
GET /users/42/posts - retrieve all posts for user with id 42GET /posts/983/comments - retrieve all comments for post with id 983This allows you to express a relationships in a different way than it is implemented, i.e. it might be useful for linkbacks.
E.g. posts tend to have an author field which references users, but not the other way round.
This can be expressed through the use of subcollections, as in the examples above.
However, you should minimize path nesting