Please don’t consider not running the progressing engine. It is there to help end users. Here is some information that will help you to better understand it:

• I recommend starting with this CSC page - Understanding the Progressing Engine: 
  https://success.planview.com/Planview_Portfolios/Projects_and_Work/Execute_and_Track_Progress/300_Work_Progress_and_Status/003_Understanding_the_Progressing_Engine
   
• There is a series of webinars that digs deep into exactly this topic, the recordings are available here - Portfolios Webinar Learning Series:
  https://success.planview.com/Planview_Portfolios/Tips_and_Tricks
   
• Based on my experience, the key fact that users, especially Project Managers, need to understand is the meaning/difference between Schedule and Actual dates and to make sure that they have BOTH of these columns in their Plan screen Column Set when working with the schedule. This is usually the ah-ha moment for most users
  https://success.planview.com/Planview_Portfolios/Projects_and_Work/Execute_and_Track_Progress/300_Work_Progress_and_Status/003_Understanding_the_Progressing_Engine/Schedule_vs._Actual_Dates_and_Durations
   
• Like any project plan, the Portfolios project plan/schedule needs INPUT on what has actually happened, so that the plan of what remains to be done can be determined. There are different ways of providing input, which you can (and should) mix and match based on your use case and the type of work. These include:
  • Manually entering actual dates
  • Using Progress as Planned (when no assignments/timesheets)
  • Timesheets
  • Automatically generated timesheets, based on planned allocations - this option is RECOMMENDED if you are resource planning but not time reporting
  • Agile Costing (where you have work delivered in connected Agile Place boards).
     
• Given that you are not time reporting, I would recommend using Progressed as Planned and then auto timesheets for the resources that are being resource managed, with probably a monthly run of the Progressing Engine.
   
• If you need more help on this topic then please ask your Customer Success Manager for some time with an expert from the Professional Services team.

To back Malcolm up, this is exactly what we do. People did get very confused, especially people building out their projects that had already started in real life and trying to put them in the Schedule columns. We did a lot of education about what Scheduled and Actual are, and reminded them often about switching to Track Progress or adding Actual Dates to a column set based on Build Schedule. Luckily, this problem ended once we were up and running and people stopped adding in-progress projects.

Another issue for training in this scenario is to convince people it is all right to leave tasks in Assumed Completed. This lets them make changes once Progression has run, if the real-life events didn’t match the schedule. Once you mark it complete, your dates are set.

In any case, this has worked out fine for us after some education of users.

After 10 years of working in Planview I will say that the biggest complaint from PMs is the “moving of scheduled dates”. This is a normal response.  Malcolm provided some great links to help educate why it is important for progression to run. Also, capturing a baseline may help as well to compare original schedule to what is actually happening. 

Sometimes it is better to first try to explain the reason for the functionality rather than turning it off. 

Good Luck

I feel you pain, and completely agree with all of the above.  It sounds like we have a similar setup and our community found it somewhat overwhelming.  It took us around 12 months to drill in some ‘good practice’ to our PM and Resource Manager community to mitigate these problems, and convince them there wasn’t some kind of Planview ‘magic’ happening to reschedule activities.  It’s not completely fixed for us, but our 4 key focus areas have been (in priority order):-

• RMs to be extra diligent when it comes to supplying resource - check the ‘Schedule Start Date’ of the requirement is not before the latest Progressing Engine date, check that the allocation aligns to the scheduled start date - when it comes to amending allocations, this may require resource views in weeks or days (hopefully a Portfolios fix this month will finally cure this once and for all!). Our RMs trying to take shortcuts to allocations has been the greatest source of ‘magic plan movements’ !!!
• PMs to hit that ‘Run Schedule’ button pretty much every time they access their plan to expose any problems and confirm nothing has moved.
• PMs to adopt suitable WBS/planning ‘types’ appropriate to their delivery - acknowledging the ‘fixed effort’ model doesn't lend itself well to tasks whose duration will need to change once requirements have been raised and can lead to lots of rework
• PMs to be aware of the impacts of constraints and predecessor/successor relationships and use these appropriately