Interesting comments. Maybe I'll end up in the minority here, but I can't imagine being happy with only one sink in a master bathroom unless I lived alone. And in my area, a decent size master bath with only one sink would be a negative factor in selling.
My vanity is only 6'-7" and there is plenty of room for two sinks. I'm baffled with wanting to sacrifice a sink to maximize counter space. As far as I am concerned, more counter space encourages more mess and clutter. Here is a picture of mine, which has enough crap on it to satisfy anyone, and still plenty of open space:
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