For the average guy with a home studio - 9 times outta 10 he gonna do irreparable damage trying to make the mix hot as possible.... by saying that a mix only need be 1/2 the volume of it's mastered version, I am pointing out that loudness is not the goal one should focus on when mixing...
For the average guy at home mixing with only plug-ins, it is best to give the Mastering Engineer plenty of headroom to work with...
As a mixing engineer it should be common knowledge that when working with 24-bit audio, the noise floor is so low (beyond the scope of the human ear) - that it would take a significant amount of attenuation to adversely affect the sound quality in a negative manner - unless the mix is too hot... then 4 or 5db of attenuation would be a great thing (the definition of attenuation means a 'decrease in level' btw lol)...
Lastly, to rely solely on a limiter to turn up the level of a song in the mastering stage would be negligent of the other tools a Mastering Engineer should have at his disposal...
If you feel the need to 'squash' ur mix, I would suggest giving the Mastering Engineer the before & after version - so that they could choose which one to work with... then evrybody is happy!!