What are the pros and cons of self-mastering?
It's not something you can explain in a post. I would say before you master your own mixes, you have to do it over 10 years before you develop the ear for one and the other. Cause the tricky bit is not only separating the processes but also learning to mix, having mastering in consideration.
So you try to aim for the best possible mix, but learning what you can leave behind so it then shines with the mastering stage, is something that takes years of practice. And if you're asking this question, take your mixes to a dedicated mastering engineer.