The process of branding is to connect ideas, descriptions and emotions to the brand, so that when a logo, or tag line or even color pallet is viewed, that the brand is recalled with its associated concepts.
Themes are very useful, because they tap into a historic and cultural body of knowledge. Let's imagine that you used burlesque or vaudeville as a theme for your brand. By doing so, you would connect your business and name with a whole slew of images that are connected with these artforms.
As such, themes are very powerful and will accelerate the establishment of your brand. For a theme to be effective, it needs to be selected early in the branding process, but brand designs such as logos, color sets, font styles and tag lines need to be derived from this theme, and the theme becomes the unifying principle for these design selections.
I worked with a sensational Domina from New York by the name of Mistress Sirene. He had been fascinated with mermaids since she was young and had a solid tattoo covering her legs which looked like mermaid scales. When I began working with her, there was never a question as to what the brand would be. Instead the question was how to best present this theme. So I searched and found a font style which was indicateive of Anciient Greek characters. We chose a color set which reminds of the ocean: Sea-Greens, deep blue, silver and an occasional Salmon as an accent. And her website was called Sirene's Grotto. For a logo, I chose to use Neptune's Trident!