When you make an effort to get as much as possible out of the photos that you take, you'll find that - over time - you have a number of night shots as well as day shots. Using a printed photo book can enable you to showcase both scenarios.
With printed photo books, what you are going to discover is that you are able to look at the extremes. Rather than showing your home town by day, contrast it with the beauty of lit fountains and glowing church windows at night. Rather than simply showing the wedding couple during the wedding and at the reception, include a few shots of them getting ready in the photo book as well.
When you're able to include a wide variety of shots - whether you shoot weddings, travel photos, or even family portraits - it is essential to show contrast in order to allow your clients (or those who purchase the photo books that you self-publish) to remember everything about the shoot. On the other hand if, rather than printed photo books that are specifically for your clients you are self-publishing photo books, including a diversity of shots shows your range.
It's the diversity that you show within your work that fully establishes you as a photographer. When you use printed photo books, you'll find that you're able to take control of marketing your work: it really is that simple.