Please see the following KB for info on start and finish dates across Clarity
Start and Finish dates on investments, allocations, tasks and assignments
In regards to the shortening of tasks and the impact on finish dates, here is what is important to us:
Simple Rules regarding changing only the Start Date of a Task vs only changing the Finish Date of a Task
'Shrinking' all Task dates does not 'shrink' the investment dates - investment dates are only changed when the task or allocation dates are adjusted to extend beyond the set dates
So extending task start or finish dates outside the investment boundaries does also stretch the investment dates, but when shortening those inside the investment boundaries then investment dates are not moved.
However, OWB can do that for you. Please see
Manually Schedule Projects in Open Workbench
For all projects in OWB, with or without autoschedule, be aware of the following relationship between task start and finish dates and project start and finish dates. If you do not set an imposed start or finish date for a project, the application sets the project start to match the earliest task start date and sets the project finish to the latest task finish date.
Imposed Start and Finish dates are attributes in Clarity at the project level. If those are not checked OWB will sync the investment dates with tasks dates. If those are checked, then the dates will be respected as they are in Clarity.