Exception for wide data rows and wide index rows

Indexes with wide rows may be useful when:

For example, if a table has very long rows, and only one row per page, a query that needs to return 100 rows must access 100 data pages. An index that covers this query, even with long index rows, can improve performance.

For example, if the index rows are 240 bytes, the index stores 8 rows per page, and the query must access only 12 index pages.