This is a good question. Let us discuss the concept of constraints in Primavera and how it work.
Mainly we have two types of constraints, start/finish on and Mandatory start/finish.
Now, both constraints will force your activity/milestone to start/finish in certain date, but what will happen if your schedule logic after update wants to change the constraints date?
Start/Finish on constraints will cause negative flow and will not shift the planned dates based on your update.
Mandatory Start/Finish will wipe out negative float on their assigned activity, and will move the activities in violation of their calculated dates.
Example:
If you have Start/Finish ON constraints and your data date exceeded this date, your project finish date will remain the same but with negative float.
If you have Mandatory Start/Finish constraints and your data date exceeded this date, your project finish date will move and there will be no negative float.
I hope my answer was clear for you, please let me know if you need any further explanation.
Best Regards,
Hany Ismael.