I recently ran across a guideline which contradicts the quiz sentence "Il est venu pour voir Sarah" associated with this lesson!!

'Venir' is purportedly one of the verbs which does not take  ANY  preposition before the following infinitive  when the context is 'come 'to do 'action of the infinitive' ! So he came to do what.. to see Sarah!  So (according to that guideline ) the preposition 'pour' is at least superfluous here if not invalid! Please clarify.