I maintain all my cars and have never had an issue when changing the trans fluid, however if it's never seen any type of maintenance as mentioned above, debris from frictions wear and tear may cause issues if it gets into places it shouldn't be. There are a lot of newer vehicles with automatic transmissions that don't even have a dipstick, and are sealed for life today. Call me picky but I have recently added in line filters to my cars as well, these get changed periodically whether they need it or not.