@Eben1 When a guest makes a Reservation Request, you are required to Accept or Decline within 24 hours. Why? Because the guest's payment method has been authorized for the amount of the reservation and this is not released until you Accept or Decline or the Request expires. They can't go to other listings until you take action. Airbnb punishes hosts who ignore Reservation Requests since it is a major inconvenience to the guest.
This does not apply to Inquiries where a simple response to a question satisfies Airbnb's response criteria. Inquiries do not commit a guest to a reservation, unlike a Reservation Request.
You should read this Community Help Guide:
https://community.airbnb.com/t5/Hosts/Reservation-Inquiry-or-Request-What-s-the-Difference-A-Communi...