There are mixed views on this, when I did a fluid flush on the E46 it was at 118k miles (approx. 190k kilometers) and the E70 was at 90k miles (approx. 150k kilometers). I also recently did a flush on my father in laws' F10 528i at 100k miles - with no issues.
In my experiences, I have only seen positive outcomes - better gas mileage, better and smooth shifting - generally automatic transmission fluids are meant to be flush around 40k mark but manufacturers market them as lifetime fluid (lifetime being about 60k miles).
Generally in drain and refill scenarios, all the fluid is not replaced anyway, you can replace 50% of the fluid - for an instance, E46 has a capacity of about 7L and I can drain about 3L and with pan off I can take another .5L for a total of about 3.5-4L, there's fluid in the torque converter and heat exchanger and heat exchanger lines, etc.
I'd recommend doing it - only use the recommended fluid. Burnt fluid has a distinctive smell to it, you'd know it's burnt (smell some fresh fluid and you'd know lol).
