In order to improve your project continuously during its implementation, you need data on which to base your decisions. These data are best provided by formative or process evaluation methods. Periodical reporting will enable you to assess the project in progress, make corrections or adjust its direction. You can monitor the process of project implementation and focus on the achievement of the objectives. Both intended and unintended (esp. unwanted) effects of the project must be observed and reported.
Important intermediate results will be presented at convenient intervals (e.g. 'milestone' meetings) and will contribute to assessing progress.
Periodical reporting can only improve the quality of the project if appropriately prepared information is given to the right people at the right time. If adjustments become necessary it must be clearly defined who has the responsibility and the competence to implement them.
Evaluation results must be presented in such a way as to be useful to the management of the project, i.e. they need to be concrete and about specific aspects of the project. What use you will eventually make of collected data is best defined early on – at least in broad terms – when you plan your evaluation.