When do I use views_get_view_result()?
Trying to give a reply to the question title:

you use views_get_view_result() when you need the result of a view inside your custom code. It works fine inside module or theme files.

For instance: you need  to get a list of users inside your custom module. Instead of querying the database with db_query, yuo can build a 
Users View named a_list_of_users and get results with

    $res = views_get_view_result($name = "a_list_of_users", $display_id = "default");


Any additional parameters will be passed as arguments.

I love this function!