The candidates only see the “accurate” (as least as accurate as the methodology says it is!) polls. Almost if not all polls released for public consumption are some form of propaganda.
Yes, polls only become public if they serve the agenda.
But be that as it is, they are educated guesses. Their accuracy is like a Bell Curve. Most are close to the middle of the curve. But some are in the tail to one side or the other. And some are skewed bell curves with more on one side than the other.
Smart campaign managers want to sell that they are the under dog in September and then they have a big mo in October. We all like the underdog.