Manual Tasks has two kinds of leaf tasks – manual tasks and automatic tasks.  Manual tasks are manually scheduled.  They should be used when you want to explicitly set a task's start and finish dates and not allow it to be changed automatically by the scheduler based on changes to other tasks. However, as in Microsoft Project, the start and finish dates and the duration are tied to one another.  This article discusses how the duration and scheduled start and finish dates of manual tasks are tied to one another, and how manual scheduling is enabled.