I started interning in a studio where the head RE would sometimes also master. i have heard its a no no to master something you recorded but he prefers it and this is why. he says he is aware of what his mastering can do to a mix and so he mixes with the intent to *fix* things in mastering. his theory is that he should have everything almost clipping its so loud while mixing (meaning limiters and compressors galore) and then turn down the master fader up to or more than -20b so that he can boost it back up in mastering. i disagree strongly with that, but i'm not an ME. in my opinion you should mix as if mastering doesn't exist. make the song sound as amazing as it possibly can without worrying about loudness too much, and then AFTER you have done everything you can do in mixing to make it fantastic without concern for loudness, you send it to get mastered. or even if your mastering yourself, your starting point should be as close to finished as possible.... but definitely 2 separate projects, not a continuation of mixing... my issue with this is, he doesnt focous on making cymbals shine, or making the kick really punch you in the face, and so while mixing, the song generally feels pretty bad, but somehow he does end up making it sound good in mastering. for all you ME's here, is this something i should be taking note of in a positive way or a "ill be sure not to do that" kind of way..?