My regular partner was N, I was NOT S, and suspect the world would double their first turn.
Given the S hand, our auction went 3♣-P-P-X-P-3♦-P-4♣-P-5♦-P-5NT-P-7D AP.
Clearly better than 4S, but we want to be in 7♠, and I didn't feel I should turn an average
plus board into a zero based on needing (on a very bad day) 4-3 spades.
Poll is (obviously) for S first bid, not for what N might have bid over 4♠ (should N have bid over 4♠)
Benefits include:
Plus... it's free!