When I was living overseas away from my parents, I always make it a point to send one to the family back in Singapore. Just so I keep them informed of my whereabouts (sometimes I travel without telling them), and also to let them know what I've seen around the city.

Now, I am back home and don't send postcards anymore to my parents, I now send postcards to my friends whom I cannot meet due to the distance (different countries, different continents) to keep in touch.