BDC Error handling technique

Hi Guys

I got an input like the following...can you please explain this----

(((A good practice is to use call transaction but use BDC session for when there is an error in the record.

i.e call transaction..

if sy-subrc ne 0.

perform form_bdc_session.

endif.

This method is quicker, you can capture errors and deal with them in a BDC session later.)))

If the records are erronious..then why to take them to a BDC session..?!!!! Any ways ..when sy-subrc <> 0 we will display them on to the screen.

Please explain.