When DRL-equipped cars are behind a motorist on the highway, they turn the rear-view mirror into a constant distraction. Sometimes moterist deliberately maladjust the mirrors so that they can't be seen, just to avoid glancing into the mirror to see what the light is all about.
When a car is behind a motorist on an uneven or hilly they go from annoying to extremely annoying and distracting. Why? Because every time the car changes angles, the light flashes directly off my mirror into the moterist eyes for an instant.
During the night time there is a day/night setting on the rear view mirror that can't be used during the day.