It doesn't replace looking around, but does expand how much I'm aware of from mirrors alone, a ton. I don't get how seeing less is better (though I do adjust them in if something's blocking the rear-view, but that's not a normal situation).
It’s a normal situation for me. I might be hauling a couple people in my back seats so their heads block the rear view. There maybe a semi truck behind me and I need to change lanes but they completely block my view out the rear view so I will only ever know that there isn’t a car in my blind spot but won’t know if there are cars in the other lane traveling significantly faster than me.
It’s not about seeing less. It’s just the fact that the rear view mirror is the most likely to get obstructed. I use the rear to mainly get a feel for the amount of traffic around me but I try to check it first then my side mirror then my blind spot before changing lanes.
