The same thing a bachelors degree does for everyone else. You've proven that you can start, stick with, and complete a task that takes multiple years and a complicated set of steps.
But a lot of the reason for this experience for me at least was that I started uni after having spent about 15 years learning to program already, and by the time I picked up again and did my masters, I'd had another 10 years of commercial software development experience.
These things are not really geared for people like us that came to them with a lot of pre-existing knowledge, but at people like my class-mates first time around that had hardly touched a computer before, and that did need a lot of hard work to come out with a good understanding of the problems.
As a hiring manager this is why I rarely care whether someone has a degree or not if they can demonstrate experience. And on the other side of the table, I only took that degree because in the UK there are still sufficiently many employers that have an obsession with degrees regardless of experience...
[0] I'm looking at you, three years of 'numerical methods', which reduced to memorising algorithms to perform by hand.
[1] I count myself amongst the absolutely useless 'applied mathematicians' from my class.