For the marketing that has significant costs (e.g., paying for ads, paying for show appearances, paying other influencers to plug, making quality videos for social media, travel for events).

But it costs almost nothing to do ARC readers for reviews and ratings, and it's free to time things for the Kindle store algorithm. You just have to know to do it, when.

And there's some other "free" marketing that publishers should have automated by now, because they can amortize that across many book releases.