In reply to UKC News: Got to say, I think having someone next to you would make on-sighting a hard bold route harder not easier. I've had successes and failures on routes that had scarey runouts where I would have told a cameraman to come rescue me if he had been hanging right there when I was on the scarey section.
When there is nobody else nearby, you can't be wimpy and call for a rescue (unless you want to hang out where you are for like an hour anyways and that usually isnt practicable) so the option to chicken out isn't there. Also means when you start the route, you don't go up with a halfarsed "well, I can get clipped in if I get too pumped on the runout bit", you start with complete commitment.
I recon it makes you more likely to succeed. But then I guess other people will have a different thought process when approaching climbs near their limit.