You can request an entity with some selected data only. You can reduce traffic, memory and CPU usage this way.
http://tp/api/v1/Bugs/?include=[Name, Description, Iteration[Name]]
Filter data by various criteria: Equality, Greater than, In, Less than, etc.
http://tp/targetprocess/api/v1/Bugs?where=EntityState.Name eq 'In Progress'
You can get more information about Entity in a single request. For example, you can retrieve Tasks count for User Story and Bugs count for User Story.
http://tp/api/v1/UserStories/?append=[Bugs-Count, Tasks-Count]
Create, Update and Delete operations
You can create, update and delete almost any entity with REST.
POST http://tp/api/v1/Projects HTTP/1.1