in MS PROJECT 2016, there is on, not so often used, field – Placeholder. Let me create new Project with three Tasks:
As you can see, Task 1 and Task 2 are Manually scheduled, and Task 3 is Auto scheduled. Now I will include Placeholder field in Gant Chart View, and I will get:
First of all, if Task is Auto Scheduled, Placeholder field is always = Yes. Furthermore, Placeholder field is read only, so you can’t change it. OK. For Task 2, and Task 3 Placeholder is Yes. Why? Well, Task is placeholder if it cannot be scheduled. So if I put, for example, 3 days to Duration field for Task 1, I will get:
Placeholder field is still = Yes, because for Task 1 we know that it will has 3 days Duration, but we do not know when will it start and when will it finish. So, I will put 21.2.2017 into Start Date for this Task, and I will get:
Because MS Project knows Duration and Start date for this Manually scheduled Task, it can calculate Finish Date, so now this Task is scheduled, and Placeholder is set to No. I will put Start and End date for Task 2, and I will get:
Again, since MS Project knows Start and Finish date, it can calculate Duration, and Task is Scheduled, so Placeholder is set to No.
So, it is easy to understand how Placeholder is set. you may wonder when to use it? Suppose that you have a Project with, for example, 750 Tasks. Some of them are Auto scheduled, and have TBD in Start date field, or duration field, etc. Those are placeholders. And, by simple filtering Tasks where Placeholder = YES, you can find out which Tasks are not scheduled yet, and they are bottleneck for finishing your schedule.Very useful Field, from my point of View.