If you remove the transmission pan more frequently. The chances of it leaking one time may grow. Not because the pan is distorted with proper bolt tightening though. Just average luck of the draw.

There are additives in transmission oil I suspect or certain charactaristics of the fluid may change somewhat over time and miles. So it is probably better to do periodic changes.

Todays transmission fluid may be superior enough or improved enough since these cars where produced to extend it a little as well. Best source of information in that regard may be the companies that manufacture the fluid. It takes little more effort really to do a more total change when you do one anyways.

Certainly if it is not a nice red color something is going on or it needs changed.