A Drupal site template combines Drupal recipes, a theme, design elements, and default content to give you a fully functional website right from the start.
Is Webhaven a Drupal site template?
Yes, by the above definition Webhaven is a Drupal site template, the term site starter or kickstarter is also often used in this context.
What is the main benefit?
Webhaven reduces the time it takes to build a Drupal site from scratch immensely and it has the tools and developer experience to build on top of it. In case you want to build a custom experience on top of Webhaven, this is up to you.
Can I see Webhaven in action?
Yes, you can see webhaven in action here.