When you take a look at the 747-400 jet exhaust velocity contours you'll see that right at the aft end of the plane you'll have exhaust velocities below 35 mph at ground idle setting. This might be an issue when taxiing down LAX's alleys but not for any other a/c or even personnel. Even at breakaway thrust exhaust velocities at the aft end of the 747 will only be around 45 - 55 mph which shouldn't be a problem either. Thermal loads at ground idle can be ignored due to irrelevance.

Myself as been walking behind a triple3 with both engines running, sometimes I've been not even behind the a/c but somewhat closer to the engines. It's a little windy up there but that's basically all.

I'm pretty sure the video of this thread was not made with the 747 at ground idle setting.

Main motivation for towing is either a) save fuel, b) reduce noise emissions or c) conserve the engines (that's why planes are towed when being moved from Terminal 1 to Terminal 5 at ORD for example - it's just more maintenance-friendly, saves fuel and so on) or d) because maneuvers are required the a/c cannot cope for without external towing.

Still I wonder what the reason might be @ Gate 80 in SFO. UAX does not count - see above. Furthermore the jet exhaust goes to the back and not sidewards so no real danger for any Dash-80, whatever, parked at 79. So I'll second the thesis that this is due to maneuvering that a 777 cannot do without external towing.

I'm being towed frequently at LHR - there they do it for noise reduction.