Hi Sarang,
The 0 booked and 16 assigned hours seems to be a bug. Which version are you using?
Typically, when a resource is booked, the capacity of this resource will be reserved to this project. It is a way to communicate to other project manager that the capacity of this resource is reserved. assignment is used for this project manager to further define how this resource is reserved to the WBS task in this project. Here is a scenario:
1. A project manager is working on a new project. As for high level, this project manager knows that he needs two developer for two weeks. So the first thing he does is to book two developers to this project so that he as reserved the capacity of these two developers.
2. Then he works on WBS to add tasks to further define how to distribute the 2 weeks hours of these two developer to the WBS tasks.
Some project manager may not use WBS but they want to reserve the resources to the project. So booking will be enough. On the other hand, some project manager will always use WBS and they will always assign resources to WBS. However, if they will make any changes like swapping the resource to different tasks within the same project, they will not need to worry that un-assigning a resource from a WBS task will release the resource as this resource is still being booked to this project.
Hope this help. As for the bug, let me know which version you are using and I may be able to lookup the appropriate KB which fix this issue.
Best regards,
Thomas