As much as possible, I avoid wearing headphones. The main reason is because wearing headphones gives me (and you, no matter what you think) an unnatural perspective on my voice. The more I think about my voice and what it sounds like, the less effective I am at delivering the message of the piece I’m reading. This is just as true for a long, highly technical training narration as it is for intimate dialog copy.
In order to concentrate fully on the story I’ve been hired to tell, I have to be able to ignore how my voice sounds and attend only to what I’m reading. And the same is true for you, even if you don’t think it is. And no matter how long you’ve been wearing headphones.
If I have to wear headphones during a session (e.g.: a phone patch or ISDN job), I wear the phones over only one ear. Again, so I can hear my voice the way it sounds in real life; and concentrate on telling the story.
The secondary reason I don’t wear headphones is because at a voice-over training session with Dick Orkin in 1997, he said, “Take off your headphones and leave them off.” And I’ve learned more about doing excellent voice-over work from Dick Orkin, than from anyone else on the planet.