[GuB-42]

I don't know the Microsoft guidelines about that. But my understanding is that apps should put their stuff in AppData.

"My ..." is for files intended for the user to access directly. For instance photo apps will naturally save their photos in "My Photos", but just the photos, and with the understanding that the user can reorganize them, open them with other apps, etc... Apps that put their crap in "My Documents" are likely not following the best practices.

Note that not all folders in %userprofile% are called "My ...". For example "Downloads" (you are not supposed to modify stuff there, just read and delete) or "Desktop" (you are not supposed to access it through the explorer). The OS won't stop you, but the fact they aren't "My..." is a hint that it is not their purpose.

[ack_complete]

Microsoft has been inconsistent, both in recommendation and what they've done in their own programs. Probably the most inexplicable is that in the Windows Vista timeframe they recommended that games place their save games into a folder under My Documents despite the Saved Games folder having also been introduced in Vista.

[connicpu]

That was often a sticking point that broke compatibility with programs between XP and Vista. Starting in Vista only programs running as administrator can modify the Program Files directory, but many programs for XP would dump config files and such directly in their installation directory. You'd have to run those programs as administrator every time or else they wouldn't work.