Originally Posted by swartzentruber
I'd say as often as you feel a soft pedal. This question is so variable based on brake fluid, track, braking technique (and obviously car). I haven't run the E9x M3 on the track, but I'd say on average you'd likely be okay doing 3 events before bleeding, assuming those 3 are in one calendar year.
Since I DIY my brake bleeds, I try to do it before it gets to that. Nothing worse than missing time at the track for something you could do at home.
3 days on my current fill of Motul 600. Let's see if I can get a 4th.