Bonnie/Lee...
PMFJI, everything that's been said by Bonnie is right on...maybe explained a slightly different way....without the 'databinding', the working datatable will not 'contain' (i.e. be 'bound to') the result of the combo selection (for example, without 'binding' to a reason code pulldown, the row of the data table being edited wouldn't 'contain' the resulting value selected by the user).
That's obviously not the only purpose, but think of it as the mechanism by which the value of the control stays in synch with what's in the data table (that you eventually wish to save).
Kevin