Give partner:
Axxxx Kx xxx Axx
Axxxx xxx Kx Axx
and 3N is cold while 4S might be down.
or
Axxxx KQx xx Jxx
where 4♠ has very few chances and 3N is big favorite.
or maybe
Axxxx xx KQx Jxx
where 4♠ has no play.
Yes, partner ...
I have posted this problem to see if people choose 4♠ (contracting for one more trick knowing that trumps will only fetch 5) or pass 3NT (risking that defenders are able to run 5 tricks of their own).