To begin with, writing a project plan is a good idea for projects of virtually every size. This is because when writing a project plan, you must think about the question of how you can achieve your project goal with the least possible risk in a short period of time, and with the least possible resources. Furthermore, you’ll think of potential problems during the planning and come up with solution approaches. This way you can respond quickly if there turns out to be any problems.
Normally, a project plan is approved by project partners, and serves as a basis for future action. Therefore it should be written at the beginning of the planning phase.
The document can also serve as information for your customers and project partners. Through a written plan they receive an overview of the separate work stages and can verify if the planning considers all their wishes. If this is not the case, you can still modify the plan before the actual project begins.
Furthermore, the written plan functions as a working tool for the project manager in charge. During the project, it helps them to maintain focus as well as adhere to budgets and deadlines.
The plan should be detailed enough so that the project manager can use this document to hand over their work to a new project manager without any difficulties. So that this can provide a quick overview, it also shouldn’t be crammed with too much information of secondary importance. The rule of thumb is: as detailed as necessary, as brief as possible.