In the GS Q&A archive with Michael Brauer, in answer to a "Mixing: vocal riding" question, he described this in a very cool way that really stuck in my head. I hope it's ok to re-post his quote here. If not, please remove it mods...
Michael Brauer's answer dated 9/21/05 (pasted here);
"I’m not sure I can explain this one in a technical way, but I can give you a kind of guide that may help.
If you make a vocal loud, the tendency is that it will sound like a vocal up mix. The vocal sounds like it’s sitting above the track and not connected. Yet, I get them loud and they feel like they’re driving the song. The answer is that you need to have little threads attached to the vocal connecting itself back to the band. I know it sounds a bit too ethereal but that’s the vision I have of it. It’s a combination of compression on the vocal, small delays, delayed plates, short plates and riding it. But it’s more than that, when you mix the vocal, imagine it’s a cork bopping on top of the water. It has to stay on top of the wave at all times. The lower the cork is floating on top of the wave, the more into the mix it feels. Giving you delay settings, and reverbs won’t do you any good so I’m not going to waste the time. It’s the image you have to get in your head as you’re mixing the vocal.
Michael Delugg taught me that image when I assisted him at Mediasound. He did all the Barry Manilow records. The first time he had me ride a vocal (no automation so it had to be just right every pass) I was lost. I couldn’t keep the vocal driving the song. I kept riding him out of the mix or getting swamped by it. So Mike had me close my eyes and imagine the vocal was just a cork floating on top of a wave. The wave being the mix, of course. It was hard, my finger would cramp and have little indentation marks on the tip from pushing on top of the fader so hard. In time, I relaxed and I could feel the place where the fader always wanted to be and I just followed the moves instead of fighting it. It doesn’t happen overnight, nothing does, but without the image in my head, no amount of mix notes on what he was using would have gotten the correct result."