Indexes with wide rows may be useful when:
The table has very wide rows, resulting in very few rows per data page.
The set of queries run on the table provides logical choices for a covering index.
Queries return a sufficiently large number of rows.
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.
