The waterfall development model originates in the manufacturing and construction industries. It is most suitable for highly structured physical environments in which after-the-fact changes are prohibitively costly, if not impossible.
In contrast, the Agile approach is different. While Waterfall methodology is sequential, the Agile approach is incremental or iterative and activities happen in parallel. Project teams spend little time on planning and more time in building and testing. The circle is also known as the Deming’s PDCA (plan–do–check–act or plan–do–check–adjust). For example, when managing a Wireless project, it is preferable to use the Agile methodology. Wireless access points can be installed, configured and tested in increments before installing all of the wireless access points. Every aspect of the stages throughout the lifecycle is revisited and reevaluated. This method allows for problems to be discovered and be fixed. Bugs are not found at end because testing could be done during the project and customer feedback to be incorporated into the design.
In summary, the use of project management methodologies depends on what type project you are managing. Agile is best suited for projects with high levels of uncertainty where creativity and innovation in finding the best solution are more important than predictability, planning, and control. Waterfall is best suited for projects that have low levels of uncertainty where predictability, planning, and control are more important than creativity and innovation.