The Resource Manager (Auto) right includes the Resource Soft & Hard booking rights.
When you have the booking rights on a resource PLUS the appropriate investment Edit or View rights, the user is allowed to add, edit, and remove allocations. The rights are not split out to isolate the ability to separately allow add, edit, remove allocations.
Reference the latest v15.2 help documentation on the personas of Derrick Joseph and Barb Hudson for Resource Management. The rights in v15.2 for booking resources has not changed in the new version. The combinations are still the same to accomplish the actions.