Of course we do low recons of the LZ. But I never, ever bet my life on being able to see every wire from a few hundred feet up, while moving at >70mph. Powerlines and telephone lines can be very small, and difficult to see while standing directly under them. I know the firefighters on the ground have looked for wires, but they can miss them, and do. Making a couple of circles and then a normal approach, assuming you've seen every possible wire, will kill you eventually.