Minor side effect is that some menu elements (back button, some text) are slightly shifted to one side - all the coordinates & dimensions are in the ini files, so it should be possible to put them all back in the right place if desired. In-game, HUD elements are positioned correctly.
If anyone is thinking of doing this I suggest changing the value to match your aspect ratio exactly to remove the stretching. This will greatly increase the misalignment and incorrect sizes but since you would be changing them anyway you might as well completely remove the stretching.