You enter relatively few pieces of information, and Microsoft Project takes care of the rest. For example, if you specify a task’s length, Microsoft Project calculates the task’s start and finish dates. Automatically. Or, if you define a resource’s workday as 8 hours, Microsoft Project can alert you if there are days when that resource will be working additional hours.
Moreover, when you change any factor, Microsoft Project recalculates the schedule so you can see the effect of the change almost instantly. Keep in mind, though, that Microsoft Project’s scheduling competence is only as good as the information you give it, so be sure your information is complete and accurate.