Soft booking is not enabled by default in Silverbucket environments.
Silverbucket has two different kinds of allocations: confirmed allocations and tentative allocations. Tentative allocations (also known as soft booking) are useful in the following cases:
A project may end earlier or later than planned. Project manager can update the resource plan by using tentative allocations and easily compare the previous plan to the new one.
Employees can mark their wishes in Silverbucket with the tentative allocations. This way every user's holiday wishes are in the same place and can easily be handled together by using the Confirm Tentatives functionality.
Tentative allocations can be used when the project continues thanks to an additional sale. For example, according to the original plan, a project will complete at the end of January, but most likely it will continue until the end of March. Tentative allocations can be used to outline the resource plan and see the overall effects in a project.
If you wish to add another layer of planning you can have the project managers create the resourcing plans as tentative allocations. These can then converted into confirmed allocations by resource managers in the software as they see the bigger picture in the Projects > Allocations views.