Don't. Do. It.
What's the difference between vanity and self? Well self publishing is indie publishing. You do it yourself. If you need a book cover you HIRE someone to do the cover for a FLAT FEE. If you need editing help, you HIRE someone to edit for a FLAT FEE. Then you publish your book and you get ALL THE MONEY the book makes, if it makes anything. These strangers don't make money off you in perpetuity.
What's vanity? It's when some scamster takes advantage of your desperation and ignorance to be published to charge you up the wazoo. Like $2000 for a cover when you can easily find someone to create a respectable cover for 1/10th or even 1/20th that. Ditto the editing. On top of charging you for everything, they will also take a cut of the money your book earns. Forever.
In other words, you're being taken for a ride, scammed, stuck, ripped off, played for a sucker. Those are the polite terms for it.
This happened to a friend of mine. I couldn't talk her out of it and $5000 later she had several thousand books in her garage that she would have had to hand-sell and that was frankly not a topic many people would care about.
And this is what Simon & Schuster has just come up with as a way to make money. It seems like Simon & Schuster is a reputable company and we'd all love to be published by them, right? They're trading on that good name and reputation to rip people off now. They probably would spin it differently, saying they provide legitimate services and guide newbie authors through the process. Yeah, maybe they do but they're so overcharging ($25,000???) for the privilege of being taken in by them, that I just have to ask one question of anyone thinking of doing this. No, it's not one question. Is it worth it? When, seriously, do you figure you'll earn the money back you've invested and get in the black?
I was contracted to write a book for Penguin. They gave me an advance of about $16,000. Out of that I bought a camera, all the supplies, paid for the illustrators, paid the agent and what all. I still "owe' Penguin $16,000. I made NOTHING on that book because I haven't made a penny back on the advance.
In Big Publishing, most books don't earn back their advance. It's writers like Stephen King and Nora Roberts paying for everything.
If you've invested $500 in your indie published book, you do have a chance that you will make your investment back and then start turning a profit. How are you going to make back the $25,000 you pay to Simon & Schuster/Author Solutions/"Archway"?
I know I couldn't reason my friend out of it. She could do the math and imagined how great her book would sell. She was a positive thinker. I am a realistic thinker. I've seen things go right and I've seen how things can go really wrong.
Don't. Go. There.