The buffer would be a useful object in the project plan to factor in uncertainty of estimates and to protect the milestones and the completion date. It would take the space between the expected completion date of - potentially many - tasks and e.g. the milestone by which they are due. The buffer object would be similar to a task as its start date depends on the tasks it dependent on, but the end date is fixed at the milestone (or at the start date of the following task). If the project is ahead of schedule, it expands, if the project is late, it contracts. The downstream schedule is only affected if the delay is greater than the original buffer.
It helps the project manager in many ways:
- she can plan for "unexpected" delays in a series of linked tasks without inflating duration estimates for individual tasks
- most delays would not affect the milestones and project completion date, but would be known to the project manager
- to provide fast feedback on the project status, buffers can be color coded on a GANTT chart indicating relative size to baseline value to highlight deviation from plan
more along this line: