Back in the day, when a romance writer would get her first Harlequin contract and an advance of $1,200, the received wisdom was to plow it all back into promotion. The idea was to create enough sell-through to encourage Harlequin to offer a multi-book contract. At that time, back end royalties for a simple Harlequin could be around $18,000, so diverting the advance to promotion efforts was not using up a large percentage of your total earnings for the book. What I've heard in recent years is that the advance is all you'll get. A far different picture, and I understand the royalty break has hardly budged this century, too.
There remain today good reasons for dealing with trad pubs: them getting your books into physical bookstores, them getting you reviews from big deal reviewers and possibly attention from big name media, and them selling sub rights--especially to film/television/streaming as well as other markets. The value of that may not have a direct dollar figure but it is substantial. But if they don't do anything beyond getting your books into bookstores, they aren't doing their full job. At a conference I went to recently, a veteran publicist said the typical publisher's publicist has 30 titles to work on at a time and job churn is major. It follows that if yours isn't the lead title that month, you're not going to get much attention at all from these overworked people. So self-publishing and self-promotion don't seem like such a bad deal after all. You probably will end up doing more for your book than the publisher would.
