WT creates a row store if the key format is not 'r'. If the key format is 'r', then WT creates a column store.

For a column store, WT generates the unique record number as the key in the table.

It would be useful to have similar functionality in a row store as well.

In many application contexts, the application generates a unique primary key, usually a numeric type. 'Sequences' are typically used for this task.

Since WT already has the functionality in place to generate a unique record number for column stores, it would be useful if this was also available in a row store.

Without this capability, when an application needs to generate a unique numeric identifier, it would have to create a separate table for this and implement serialisable isolation at the application layer for this capability.

This thread on google groups has a little more contextual information
https://groups.google.com/forum/#!topic/wiredtiger-users/r1K5AchwE3E