The Date Intelligence and Adventure Works Sales tables only serve to provide an intuitive name for users to find related DAX Measures. For example, several of the most important DAX Measures of the dataset will include both Internet Sales and Reseller Sales. It wouldn't make sense for these consolidated measures, such as Total Net Sales, to be found under the Internet Sales or Reseller Sales fact tables in the field list. For similar usability reasons, the Date Intelligence Metrics provides an intuitive name for users and report developers to find measures, such as year-to-date, prior year-to-date, and year-over-year growth. The two parameter tables, Date Intelligence Metrics and Adventure Works Sales, effectively serve as display folders, as shown in the following screenshot of the Fields list from the Report View:

To obtain the calculator symbol icon in the fields list, all columns have to be hidden from the Report View and at least one DAX Measure must reference the table in its Home Table property. Once these two conditions are met, the show/hide pane arrow of the fields list highlighted in the image can be clicked to refresh the fields list.

In this example, the Adventure Works Sales and Date Intelligence Metrics tables both contain only a single column (named Dummy) that can be hidden via the right-click context menu accessible in the Relationships View, the fields list of Report View, and for import datasets the Data View as well.

The columns of the three fact tables (Internet Sales, Reseller Sales, and Sales and Margin Plan) are also hidden to provide users with an intuitive display of groups of measures at the top of the fields list followed by dimensions and their hierarchies. 

The Home Table for a measure can be set by selecting it from the fields list and choosing a table from the Home Table dropdown on the Modeling tab in the Report View. As shown in the following screenshot, the Internet Net Sales (PY YTD) measure is selected and Date Intelligence Metrics is configured as its home table: