I've heard a few mixers say that by creating an exact copy of the lead vocal track (efx and all) and blending them 50/50 during your mix can improve the sound of the vocal. I am wondering what everyone (esp. Warren) has to say about this technique.
An exact copy only makes the track louder. You would need some kind of processing.
What Warren does is his "Vocal thickening trick" where he detunes, delays and pans copies of vocal tracks.
There a some plugins that will do similar.