I've taken a few days to think of the best answer for this question, and the best I've come up with is there really is no "right or wrong" here, only "quicker or longer".
But first, lets take a walk into the past.
Back in the "old" days, the division between editor and re-recording mixer was very defined. With the sound for film originally being edited on magnetic film, there wasn't much the sound editor could do to manipulate the sound other then a partial fade by actually dissolving the magnetic oxide off of the film with acetone. Even adjusting the levels during the transfer process weren't a great option because if you were too low, there would be too much hiss, or on the other side if you were too loud it would create distortion. With the sound editor only being able to actually hear a few tracks played back at once, their primary job was to find the sound and place them in sync (not an easy task).
The re-recording mixer had the luxury to listen to all the tracks together and was their job to balance them all together. If there was a problem with a track, or something needed to be added, the mixers hands were tied. The tracks would be taken off the machines and sent back to editing.
As we walk a bit forward in time, multitrack tape machines made the sound creation job easier, and more creative. The overall track counts started to increase. Unfortunately on the dub stages, the re-recording mixers had to start pre-dubbing tracks in order to be able to play them all back at once during the mix due to the available real-estate on the consoles. This led to bigger consoles and the invention of mix automation.
Fast forward to today - (what in the heck is tape?)
With both editorial and the mixer using the exact same gear the lines between the two positions are becoming very blurred. DAW's have given sound editors the ability to literally create hundreds of tracks of audio. They have also given the re-recording mixer the ability (along with new digital consoles and control surfaces) to play them all back and manipulate them without extensive pre-dubs.
This is where quicker and longer comes in.
For the sound editor it obviously makes their job longer to automate volume, pans, and sometimes even reverbs to their tracks. Most editors I know prefer this because they have been working closely with the Director and the sound supervisor anywhere from 4 to 12 weeks. When the session leaves them, they know the tracks will be at least listened to once the way they have intended them to play. While the re-recording mixer has the ability to change anything, they can focus on the balancing of the elements to work on the emotions of the film and make sure it flows properly.
If the tracks have no automation and is left up to the re-recording mixers to weave through them, the final mix will take longer. Longer on a mix stage equals money.... a lot of money. You can generally get one week in an edit suite for the cost of one day on a mix stage.
Like I said at the beginning, there is no right or wrong. As a re-recording mixer I can see it both ways. If the tracks come to me with volume and pans, its great. (My wife likes this as well because I'll be home for dinner earlier) If the tracks come to me with nothing though, I also enjoy it because I get to really mix a lot! (Mixing is fun...and that's why we all do this right?)
Some people don't want me messing with their stuff, others gladly welcome it. Like I said there is no right or wrong. All I ask is that it's in sync! :)