There are MANY reasons why adopting a project management methodology for your project is vital, however here are our top three reasons:
1 - Team
Without some sort of framework to a project, whether it be waterfall, agile or however you determine your project should be managed, you need to have some way of showing a structure.
If you don't, it's chaos. No one team member has a firm understanding of their role within the project. In actuality, you don't really have a team unless there are working agreements in place. The working agreement is there to determine how everyone is going to work together to complete the project and meet deliverables.
Without guide rails or parameters to understand how everyone is working together, there truly is disorder and you really don't have a team without those connecting components. We all know that projects without a functioning team have a limited chance of success.
2 - Making It Easy
Equally important is to make things as easy as possible for your team a.k.a. subject matter experts. Providing a framework enables organization and makes it easier for them to operate within the parameters of the project methodology.
If Waterfall is the methodology they are accustomed to, then setting up a waterfall based project would allow them to function more efficiently as a team. The same applies if Agile is the framework that would provide an easier project path.
Having a working agreement and an understanding of what tools and processes should be put in place to make the working environment easier is very important.
3 - Reporting To Leadership
Reporting to leadership without a structure in place or project management foundation is an inefficient way to report to leadership.
For example, it makes if difficult to answer questions like: Where is the project at? Where do we expect to be? What are our goals throughout the project? There needs to be some way to report this information.
In order for leadership to make executive decisions, they need to know the triple constraint (scope, schedule, budget) of a given project, which is best provided with a solid project management structure in place.
While it may seem adopting a project management methodology can be a casual decision, it does need to be well thought out and executed to be 100% effective and positively impact project goals.