You should use a non-standard modify operation when you want to update a subset of the attributes on a database record or records. Non-standard modify operations use a key that you specify to locate the target records, and this may result in multiple records being updated. You also specify which attributes of the entity are to be updated.
Non-standard modify operations can be more efficient than standard ones because they result in less database I/O, and the database may not have to update as many indices as would be the case for a standard modify operation.