The missus's mini does it, my work van does it and the E63 will do it, it's second nature to us now.
It can seem pointless in some situations when it is only stopped for a second or so, but when you're stopped for a while its nice and quiet and kind of tranquil, music takes on extra clarity when the engine is off.
Although it does have a modicum of intelligence, it only works if the engine is warm, is isn't too cold or hot outside, battery OK, air con isn't working hard etc etc.
If auto-stopped it will re-start after a minutes or two anyway if battery volts drops (winter. lights on etc) or air con / heating / servo vacuum requires it.
It can be a pain if you pull up and it auto-stops, but then you get out (to open a gate for example) this cancels the auto-start, so when you get back in you have to go throught the whole ignition off (thus phone off/music off) / re-start procedure.