Time for a confession...
I`m one of those who leaves them on from engine start to shutdown
I do it for 2 reasons really...
1)They DO make it easier for other people working airside (who your most likely to injure) to see the a/c - been told that by the engineers,refuellers,other pilots and even the local ATCOs.
2)They look cool.
Oh yes,perhaps the pilot who stopped suddenly whilst engine was at high rpm was actually testing the brakes?