This week, I'll be discussing some of the cons of a publishing company. These, though, apply to publishing companies that aren't strictly online publishers. One of them is that publishing companies can be extremely expensive. Back when I was in high school, I sent one of my stories at the time into a publishing company, and my manuscript was accepted. For the company to publish it, though, (this was also without editing services) it would've cost me $8400. Being a high school student about to enter college, that wasn't realistic, so I had to decline the offer. So unless you have an established income or some of your family is willing to pay for the expense, it's hard to accept a contract with a publishing company. Granted, I received that price five years ago, so things might've changed, and that price was only one company. Other companies might be cheaper, but just be prepared that some companies may charge you a lot of money for their publishing services.
A second con is the contracts. Make sure you read it very carefully, so you know what you're agreeing to. The company above had a contract where they could terminate it at any time they wanted, especially if the book didn't sell so many copies in a given time span. Also, my percentage of profit on each of my books would've only been ten percent. So if a book sold for ten, I would make one dollar. In order to make my money back, I would've had to sell at least 8400 books. If I didn't sell that many and only sold a few copies, my contract could've been terminated, and I would've just lost a significant amount of money. Those odds didn't look too favorable, especially when I had college bills looming over my head in the near future.
Thirdly, a publishing company may try to pressure you into including or taking out content in your book to fit their image, not your own. This is why it's important to research a publishing company before you agree to sign a contract with them. Their values might not fit your own, and you may find yourself in a position where there is severe value conflict. A good way to know what values a publishing company supports is read over their website in depth, check what some of the books they have published before are and what the content of those books are. Anyway, I hope that this helps!