Yes. It is important you know the purpose of writing and producing your book, so you can choose your target market and start building your community.
You can start engaging with your audience months (and even years) before you publish and start marketing your book!
This applies to both self-publishers as well as authors seeking a traditional publishing contract. In fact, if you are seeking a traditional publishing contract, your publisher will want to know what you have created for your readers as an additional complementary resource, to engage them further in their reading experience.