Work Breakdown Structure in Theory
Unfortunately, too many academics and academic textbooks teach the work breakdown structure as a big "to do" list. They ignore the impact on the PMs ability to track progress and make good assignments. Many people who have taken these project management classes spend very little time learning the work breakdown structure and, as a result, think it is just a list with "to dos" for every team member. The results are disastrous as we will discuss below.
Work Breakdown Structure in Practice
In practice, many project managers follow a "to do" list approach as discussed above. The result is that their assignments for the team members are vague and the performance expectations are unclear.  On those project teams the estimates are always inaccurate because it is very hard to estimate the work or duration of a "to do" list item when the deliverable is too general.  As a consequence, the team members are guessing about what is expected and routinely have to redo assignments when their guess doesn't meet the current performance expectation of the project manager.  It is this "to do" list approach to the work breakdown structure that is one of the major causes of the overall 70% project failure rate.
WBS "Best Practices"In the Real World
In the typical situation project managers face in the real world, we have no formal authority over the team. But one thing we can do is decompose the work breakdown structure into a measured definition of success on each deliverable.  No matter how limited our authority over the team, we can still follow best practices on the WBS.  We start from the overall project acceptance criteria which is a measurable definition of success.  Then we continue the decomposition,  identifying the major deliverables and defining success on each one in quantified terms.  We don't want to have to guess about whether we produced the right deliverable, we want to be able to measure it at the end of the work.  As an example, a task such as, "improve service on customer phone calls," is a typical "to do" list item that might be included in a work breakdown structure. It makes a terrible assignment and invites scope creep. On the other hand, if we decompose our deliverables properly, that work would have a metric defining success such as: "95% of the customers experience hold time of less than 15 seconds."  It is difficult to come up with these measured outcomes primarily because we have to decide exactly what we want.  However, the benefits are enormous in terms of more accurate estimating, more confident team members who know what success is before they start work and tighter control of the scope because the precision of these definitions helps us keep out unnecessary work.