EEXIST. Lots of IO operations can fail because the destination already exists, and in quite a few cases, this isn’t really a failure so much as just a different outcome. In general, there is quite a bit of code that wants to branch on the specific error reported for an I/O operation.

Also, database errors. While the specific error may not be important, knowing whether an error means that a transaction definitely did not commit is valid, as is knowing whether retrying the transaction is likely to be useful. (The common case is retrying transactions that failed due to deadlock.)