For example, if the cue phrase Besides occurs at the beginning of a sentence and is not followed by a comma, as in text 9, it usually signals a rhetorical relation that holds between the clause-like unit that contains it and the following clause(s).
if the same cue phrase occurs at the beginning of a sentence and is immediately followed by a comma, as in text (10), it usually signals a rhetorical relation that holds between the sentence to which Besides belongs and a textual unit that precedes it.