For connecting domestic flights, you almost never have to exit and reenter security, though there are some exceptions at airports where the terminals aren't all connected. For domestic-to-international connection, it's still pretty rare that you have to exit and reenter security, even if you're changing terminals.

You do not necessarily have to go through security at every airport, as it depends heavily on your itinerary and the airport's design. For most domestic-to-domestic connections in countries like the United States, you remain in the "sterile" area and can walk directly to your next gate. However, if you are arriving from an international destination, you almost always have to clear customs, collect your bags, and go through security again before your next flight. Some countries, like India, require security re-screening even for domestic connections. Additionally, if your connection requires you to change terminals that are not connected "airside" (behind security), you will have to exit the secure area and be re-screened at the new terminal. Always allow extra time for these scenarios, especially when traveling through major international hubs like London Heathrow or Dubai, where terminal transfers often involve additional security checks.