If I am mastering my own mixes (or mixes I have made from raw tracks submitted by clients) I will do my mastering within the project on the "master bus" so that if required I can go back to the original mix and tweak anything "on the fly" rather than trying to "fix it" in the mastering
PCs are so powerful nowadays I think the lines between mixing and mastering can be blurred a little
Incidentally, I now have a great mastering chain saved as a Pro-Channel preset, which I can load in to any project or use on a stereo WAV
I basically have one instance of Ozone 6 set up with eq, exciter, dynamics, imager --> then I have the option to use the tape emulator (or other fx within the pro-channel using fx chains) --> then I have another instance of Ozone 6 with the post-eq and maximiser
This setup allows me to add fx "within" the Ozone 6 change without having to run it in standalone mode
The only thing I lack is the volume matching bypass feature of Ozone as I need to bypass everything, which I would like to do in one click but I can't add pro-channel buttons to groups