It emphasizes the prevalence of the countless hardships that FDR witnessed out west.
Explanation:
Beginning sentences with the word 'I saw' signifies that one was a witness to a particular incident. That is the informatuon of what transpired wasn't a relayed message from another source but a firsthand account of what happend. The repetition of the word also indicates persistence and hence continues to draw the attention of the listener to the account of the event being relayed. Similarly, the word being repeated and given by a firsthand witness will continually call on emotions which might help in effective conveyance of the message being passed.