What is an example of Task Sequencing?

Here is an example of Task Sequencing:
Consider you have a parent task with three subtasks.​

You add a previous task to Subtask 1. Subtask 1 can be marked as Completed only after Previous Task is completed. In this case, the start time of Subtask 1 gets updated to 6:30 PM. 

Subtask 2 and Subtask 3 run independently of Subtask 1 and Previous Task. However, Parent Task can be marked as completed only after all subtasks are completed. The start date and time of Parent task is set to 5:15 PM and its due date and time is set to 7:30 PM.