I use Preen on our perennial beds and shrub borders. I think Mrs. BD, the Weeder-in-Chief, appreciates it, but my Mom gives me heck for using it since she views it as lazy and possibly not environmentally acceptable.
As I understand it, it mainly prevents seeds from germinating. What's wrong with that? Yes, we mulch too, but seeds germinate in mulch.
Weeding plantings to make fresh space for the new weeds no longer interests me. I'd rather be playing tennis.