Keep in touch

I have always heard my friends and sometimes myself end conversations with these three words "Keep in touch". What does this keep in touch really mean. What do we really mean when we ask them to keep in touch.

I always wondered how often should you call or talk to your friend to make sure you stay in touch. Conversations with friends are a never ending process and no matter how much you talk to them, you know there is always something thats left out and you need to start another conversation to finish that one. Its a never ending process. The closer the friend is, the more you need to talk to them and discuss your life with them. If its the closest friend then he needs every detail of your personal life as well.

At the end of the day no matter how much you talk to them, does all the talking qualify as you staying in touch with them or am I over doing it? This question is way beyond my intellectual ability.