At the bottom of the page, there's a menu that lets you share your legislative district (LD) with TAN if you want to. TAN uses this to decide what legislator to contact and customize the script.
For example, if it's about a committee vote, for example, the mail will go to your legislator on the committee if you have one, otherwise to the Chair. That's usually more effective then sending email to your own legislator who's not on the committee.