There have been many discussions on this topic. Do a search.
To answer your question, though BMW says it is a "lifetime warranty"
in my opinion, it is prudent to change the filter and fluid around 100K miles, if not sooner. When I changed on my '97 328i recently, the
original fluid looked fine. I consider changing the [transmission] filter and fluid as an insurance... relatively cheap insurance.
If you'd like to keep your car for a long time, it's a good idea to change.