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.
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