This week, I'll be discussing some of the pros of a publishing company. One of the first ones is that you don't have to do everything yourself. You have a team of experts who can work on a professional cover for you, edit any spelling/grammar errors, etc. This gives you more time to focus on your writing and your other commitments.
A second pro is that they will do marketing for you to. They'll connect you to their contacts, who can bring your book(s) more notice. You don't have to build up a reader base beforehand, though it still helps to know your audience for your work, and you don't have to worry about paying money/posting your book(s) on multiple sites in order to advertise your book.
Another pro is that distribution of your book to various bookstores is easier. This ties in with marketing since it involves advertising your book to various booksellers, who might want to purchase hard copies. Booksellers see the publishing company label, and they're more likely to trust that the book will sell in stores. The company also can work out negotiations to make the book(s) more affordable to stores, and this might be harder if you're self-publishing. Anyway, I hope that this helps!