The ability to choose an existing theme among thousands of free and premium themes is one of the reasons for the success of WordPress as a CMS. Using an existing theme dramatically reduces both development time and cost, as opposed to designing the site from scratch.
The primary intention of a theme is to function as the presentation layer of the site. However, WordPress has evolved into a state where a basic theme, designed to act only as a presentation layer, no longer works. As a result, developers are including more and more advanced functionalities and logic within their themes to compete with other themes. In modern sites, the developer's role may involve customizing theme design, building themes from scratch, and even creating application-specific themes. Therefore, we need to be aware of the type of development involved...