You can use four types of task dependencies (or links)in Project to define the relationships between tasks in your Project plan.
If you link tasks, Project will automatically adjust your schedule when any part of your plan changes.
If instead you enter specific start and finish dates for tasks, you override that automatic adjustment. Whenever anything changes, you'll have to make updates by hand — and you'll have to remember to update your plan every time.
So you see the advantage to understanding how Project dependency types are used to link tasks. With four simple types, shown in the picture, you can create plans for a wide range of situations, and your plans are ready to embrace change.