Should I Advertise Book One if I Have Nothing Out There?

Some say you should advertise even if you don't make a profit, just to build up a reader base. I usually do at least some advertising on the first book a normal itll be smaller, one punched things like boosted posts and featured posts. Building a readership is always a good idea, but only if it's through newsletter subscribers. Becauseit' too hard to keep them excited about your books if they don't have a way to contact them direct an directly for subsequent books. But yet, with just one book, is hard to come out on top.