What is the main function of the parasympathetic nervous system?

The main function of the parasympathetic nervous system is indeed to decrease bodily activities. This branch of the autonomic nervous system is often referred to as the "rest and digest" system. It promotes a state of calm in the body by facilitating processes that conserve energy and restore body functions after a period of stress or heightened activity. For example, it slows down the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles in the gastrointestinal tract.

In contrast to this calming and restorative role, options related to increasing heart rate or enhancing the fight-or-flight response pertain to the sympathetic nervous system, which prepares the body for stressful situations. Transmitting sensory information is a function primarily associated with the sensory nervous system, not specific to either the sympathetic or parasympathetic divisions.