So I've been reading a lot about the Joey Sturgis method lately and to me its very interesting. Particularly the idea that he does everything himself, including mastering. Conventional wisdom in the audio engineering field seems to be that you should always have someone else master your music if you want it to be of the absolute top quality. Sturgis' argument is that having control of the entire process, end to end, gives him more control over the sound of the production. He follows up by saying that often mastering issues are actually deferred mix decisions. This part of the argument i've heard from the same people who say its a terrible idea to master your own music but to me its much easier to fix the mix issues if you still have access to the mix. Sturgis also states that he works with his mastering chain largely in place and treats the entire process as moulding a piece of clay. The mix is less a series of process steps and more an unfinished production that works towards being complete. When its done, its done - mastered and all.
As with all things I feel there is a balance to be sought. There are different mindsets for different problems with audio production and the mental blurring can be a bit disruptive if you aren't careful with it. That being said, the idea of mixing and mastering at the same time is quite liberating as you avoid the jarring "My music doesn't sound loud enough" towards the end of the mix process. If you want to read more I recommend the sound on sound article below: