Site templates are guides you can use to pre-fill information when you add sites. These templates are not required to create sites; however, they can make creating multiple sites easier and faster by establishing the services you want to assign to sites when you create them.
Each template can include different configurations that satisfy specific business requirements. You can create as many templates as you need.
There is no ongoing association between templates and sites; templates are used simply to define the initial settings of the site. For example, if you add a site then later change the template you used when adding it, the site is not changed.