Disadvantages of external lists in BCS

-Approval of items is not supported.

-Attachments are not supported directly.

-Check-in and checkout of items are not supported.

-Using standard site content types in External Lists is not supported.

-Drafts of items are not supported.

-Send-To operations are not supported.

-List event handlers are not supported.

-Datasheet View is not supported.

-Querying through LINQ to SharePoint is not supported.

-Document templates are not supported.

-Versioning of items is not supported.

-Starting workflows from items is not supported, but workflows can read or write to External Lists through the SPList object.

-Validation formulas are not supported.