MDAC 2.5 SDK - OLE DB Programmer's Reference
Chapter 6: Getting and Setting Data
Row accessors can be optimized. How this is done is provider-specific. It is usually faster to use an optimized accessor than an unoptimized accessor. For example, the provider might structure its internal row buffers to match the types used in the accessor. Optimized row accessors must be created before any rows are fetched.
Flagging accessors as optimized affects only providers that support optimized accessors. In general, providers are not required to recognize optimized accessors nor are they required to enforce any of the restrictions associated with optimized accessors.
Clients written to consume data from general OLE DB providers should never include the same column in more than one optimized accessor, and for all bindings to a particular column, clients should use a data type coercible from the type specified in any optimized accessor for that column.