Ranch dressing, nacho cheese sauce, chocolate syrup, and caramel dip all have high water activity values. What keeps them safe? Combining good manufacturing practices with either low pH or water activity (or both). The primary quality measurement on sauces and dressings is usually pH, and many are acidic enough to control microbial growth without help from water activity. Still, water activity can act as a secondary hurdle to microbial growth, providing an extra barrier against potential problems.
Jams typically have a lot of sugar in them, and depending on the fruit ingredient, may also be acidic. In less acidic jams, water activity acts as the critical control point because sugar's ability to lower water activity prevents the growth of microorganisms.
Quality control in sauces and dressings requires getting readings quickly, and confirming products are in spec. The AquaLab 4TE gives readings in under 5 minutes, and without sample preparation.