This article will help you understand the benefits of building a Custom WordPress Theme instead of using a far cheaper Template Theme.
Customization. Do you want to be unique, or do you want another business to have the same site as yours? If you don’t care about being unique, then if you can find a a WordPress Template that can look like and behave exactly how you want it to, go for it. However, you’ll have trouble in the future when you want to make adjustments to how pages are laid out and how elements behave when you interact w/ them. Your ability to highly customize a template (safely) is minimal.
Security. If you were a hacker, would you spend time hacking one site at a time, or would you hack a template that would immediately give you access to thousands of other sites on the web using the same template. Enough said.
Stable. WordPress has 4 major updates a year. The plugins you run on your site and the theme that runs your site all interact w/ WordPress… the more moving pieces you have the more points of failure when something goes wrong on your site (this is also why we don’t like using many plugins). In WordPress version updates, they integrate the newest versions of many software that’s used (php being used, jQuery, tineMCE, etc.)…. some times templates don’t update… and if you update WordPress and it’s not compatible w/ your theme then… KABOOM!
High Performance. Templates are made for thousands of users… they need to have hundreds of options…. templates are usually very bloated… a lot of unnecessary pieces of code that are never used. This just makes the site perform slower and, when your website has an issue w/ upgrading a plugin or wordpress, it cause thousands of more points of failure… It’s easy to diagnosis an issue on a custom site than a template.