When you want to lock the schedule of a task with dependencies, Project Insight has you covered! We've now implemented a way to ensure your schedule is followed when you've got user permissions which allow schedulers to change tasks in such a way that would cause undesired actions further down the chain.
This task you're locking is not required to have any time constraint. This example below has one for simplification of explanation. Locking the task is to ensure that any modifications which change it's schedule are not possible.
Here's a more simplified explanation of a situation where this would happen.
Task A, B, C, and D are all on a linear succession path and when D is completed, E can be started. To meet a deadline, Task E takes 10 days and must be completed on 3/31/20. See screenshot below:
If one of our trusty resources was to fall behind on Task B and move the date back as seen here:
...the consequence in doing so would move all successive tasks backwards and we would not make the 3/31/20 deliverable despite the "Must Start On" constraint!
To prevent this unintended push from happening, you need to lock Task E with this new feature called "Lock Scheduled Dates" found in the Task Edit (full) on the Advanced Tab.
Lock the Scheduled Dates for the task.
Now, when you or your trusty resource planners attempt to push back Task B, they receive notification and the action is no longer possible because it unfavorably pushes Task E.