Potato flakes are good at retaining moisture, keeping bread soft for longer. Even though they're dehydrated, they will rehydrate once incorporated into the bread dough.
Use about a ½ cup or a ⅓ cup of the flakes for every 3 cups of flour. It's enough to improve the bread dough without significantly impacting the loaf's flavor.
The potassium in potato flakes may also lead to a faster rising time for the dough. This is because when potassium interacts with yeast, it gives it a boost in rising power.