I listen to music while training inside, but never outside.

First, for safety. I want to listen for autos, other riders, dogs, and heaven forbid, perverts.

Second, for habit. Music is forbidden in USAT triathlons and I want to train as I will race.

Third, to hear the sounds around me. I want to hear the wind in the trees and the river roaring as I ride up the trail.

My 2 cents