Use when AdHoc is enabled or you want to test remote pivoting/file reads.
Check
SELECT name,value_in_use FROM sys.configurations WHERE name='Ad Hoc Distributed Queries';
File Read / Pivot
SELECT * FROM OPENROWSET(BULK 'C:\Windows\win.ini',SINGLE_CLOB) AS x;
SELECT name FROM OPENROWSET('MSOLEDBSQL','Server=10.10.10.37;Trusted_Connection=Yes;','SELECT name FROM master.sys.databases');
SELECT * FROM OPENQUERY([LINKNAME],'SELECT DB_NAME() AS db,@@SERVERNAME AS srv');