In my opinion, it's very challenging nowadays to use just 1 methodology in managing a project. Again, it also depends on the industry. However, bringing both together can come in a great value to the project. Being able to apply Agile to uncertain aspects and Waterfall to fixed deliverables means having a flexible project that’s better built for success. Mixing project management methodologies allows your team to plan projects with both flexibility and structure. The goal is to reap the benefits of both project management styles without the weaknesses of either.