Good question!
When you save form geometry to a cfg file or registry the values are written in units of the current ppi of that particular system. When you later run the project again on the same machine with the same ppi the form will have exactly this size.
Somebody else on a machine with different ppi stores the geometry in his written in his ppi. He will write different numbers than you, but due to his different ppi he sees the form at the size stored upon reload.
So, when both config files are distinct, everything is fine. And this is the normal case: every user writes his own cfg to his own machine.
But when both users share the same cfg file, for example, because the cfg is stored on a network drive, you must be careful because every user interprets the stored numbers in his own ppi units. Even if nobody changed the form size one of them will be surprised because the form when reloaded will have a different size than when the application was closed.
So either don't share cfg files, or write the current ppi to the cfg along with the dimensions, or rescale the dimensions to standard ppi, say 96 ppi (using the Scale96To***/Scale***To96 functions).