I noticed this today with someone trying to File ... export to STL. The exporter is taking the tessellation value from the View property of a solid. So if you wanted a finer tessellation STL output you can just change the value for an individual object, and recompute then export.....so far OK.
However the user was complaining of it working sometimes and not others, at first I incorrectly thought Part WB objects were still using the tessellation in Edit..preferences...PartDesign... Shape view...Tessellation.."maximum deviation depending on model bounding box"... but then I eventually worked out what was going on...
FreeCAD is fighting between default and custom values for that view deviation property.
If you change the preferences value, it changes all your existing objects deviation values to that new value regardless of your having set a custom value or not for any specific solid.
what makes this worse is that even if you don't edit that value in preferences but you do change any other totally non-related preference value and click OK, the deviation properties of all your objects get changed to whatever value was already in that partdesign view tessellation setting without you being aware of that.
If you edit the view property value then that new value gets saved to the file, but if you adjust any other completely non-related property or even none at all but press OK button in the preferences editor you get the deviation value from preferences pushed into all your deviation properties and that new value then gets saved in the file.
I have tested in the two versions below.
let me know if you don't understand what I am talking about.
I think you would commonly notice this when either exporting STL files via the simple File menu exporter or if you had set a low value for a slow to recompute complex model.
Jim
OS: Ubuntu 18.04.3 LTS
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.3.
Build type: Release
Python version: 3.6.8
Qt version: 5.9.5
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/Australia (en_AU)
OS: Ubuntu 18.04.3 LTS (KDE/plasma)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.
Build type: Release
Python version: 3.6.8
Qt version: 5.9.5
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/Australia (en_AU)