In agreeance most of what rachelpatel1796 said above, I believe that the project execution phase (especially the controlling aspect) is the most important stage of the project cycle. The need for strict compliance to key performance indicators as well as carefully monitoring/ managing the various costs and time spent is paramount in seeing out the project though the longest part of its life cycle. This is primarily due to the tendency for scope creep to begin to take effect and this could have devastating consequences. These changes, although they may seem subtle at first, will snowball into project altering proportions and unnecessarily siphon funds away from the profits. In extreme cases, vision of the original project could potentially be completely lost and the project becomes one big money pit with no direction; embarrassing the parent company and employees alike. In addition, although no one part of the lifecycle is unimportant, if a decision had to be made, I would say that the closing of a project is least intensive if the rest of the project was executed correctly. When the rest of the project is run the way it was initially intended (rarely happens in industry) closing is filled with the documentation of the projects and aevaluations of what was most effective and ineffective for present, and future learning.

I have included a really helpful link below that further dive into each of the stages of the management cycle and all the components that comprise them. http://www.method123.com/project-lifecycle.php