Setting a table header row allows you to delineate between the table and header regions of your worksheet.
When working with spreadsheets, we often add general information to worksheets above our table rows. In Spreadsheet.com, we call this region a header. Headers can be used as a banner, display important metadata, highlight summary statistics, and more. For instance, rows above this tabular region might contain information about a project name, owner, overall timeline, etc.
Adam Steinfurth at LearnSpreadsheet.com has written an article and created a more detailed video about using Table Header Rows in Spreadsheet.com:
For a more detailed introduction to data types, check out our Quick Start Guide article on Worksheets, Data Types, and the Table Header Row. Or dive into our full suite of articles on Tables and the Table Header Row for more on working with the header and table regions.