I was told a couple of years ago by a BMW tech (yeah, I know) that the wipers "auto-calibrate" on the first couple of sweeps, so if you're finding them not reacting to the rain well enough, switching them off and on again will force them to re-calibrate.
On my E46 this did seem to work, although it may just be placebo effect. So far my F30 has been fine, but it's worth a try if you've got this problem.
I'd be interested to hear if this has any effect or if it's just snake oil
