The re-evaluation process examines the accomplishments of all users enrolled in an org unit with the Can be Evaluated permission. Depending on the number of users included, this process might be resource-intensive.
You can configure your system to automatically re-evaluate progress every time an applicable change is made, or you can disable this feature and require users to manually initiate re-evaluation on out-of-date elements. Using manual re-evaluation allows users to control when the re-evaluation process takes place. This will help you to manage server load if you instruct users at your organization to postpone re-evaluations to non-peak times.