in one of my previous post I have explained Driving Tasks in Microsoft Project for the Web. Now I will show you how this effect Task which has % complete greater than zero.
First, I will crate new Project:
and in Timeline View:
Obviously Task 2 is Driving Task for Task 3, as it can be seen here:
Now, let’s say that Task 3 is 50% completed:
As you can see, Task 2 is no longer Driving Tasks for Task 3. Why is that? Because when Task has been started (as in my example, Task 3), it will not be moved even if, for example, Task 2 has extended Duration. Let me show you that. I will put 7 days in Duration field for Task 2, and I will get:
As you can see, Task 2 (and Task 1, too) has no impact on Start Date for Task 3, because it has been started (e.g. it has some % completeness). And therefore Driving Task for Task 3 doesn’t exist anymore.