I think what he's trying to say is what if the final mix down that you make sounds good to YOU, but once the Mastering engineer takes hold of it, it sounds like complete $hit to him and unusable to him. For example, lets say your using some basic Logitech or whatever PC speakers and to you it sounds aight, but once it hits those very high quality studio speakers it sounds totally different and $hitty. Or for example, lets say you panned an instrument too far to the left or right thinking it sounds cool or good enough, but to the mastering engineer it sounds like crap or isn't neccessary. So what I guess he also wants to know is, how do you arrange your mix so it pleases the engineer and makes it easiest for him to "fix up?" Do you adjust the mix before hand to how YOU think it sounds good, or do you just leave all the sounds at the same volume level, no effects, no panning, etc... That's why I think he's asking, isn't it better to just split the individual tracks all at the same maximum default level, no effects if neccesary, no panning, then the engineer can decide himself how to arrange those settings when he builds it all together???
I always wondered the same thing.