WBS is defined as the work that is required to produce products. It is a hierarchical division of work into subparts. It works as a foundation step in project management. According to me these can be broken into two options 1)break down into design product, development product, test product 2)break down into regulatory, marketing, clinical, engineering. So here pitfalls can be using which option, than ofcourse time and communication also plays an important role because if there is no communication the project will take more time and you would not be able to work according to WBS. So for successful WBS person needs hard edge measurements.