Compared to Context, Call Templates allow for more control and can also execute sequential actions in the background, invisible to users (e.g. to perform a ticket-creation while triggering a status update).
Context has no functional reliance or dependency to either service or direct call templates. Both features can be used in combination or standalone. ☝ However, be aware that your users might get duplicate websites opened when they are defined as context / templates and assigned on both service and user level.