A diary is a place where you can write your feelings down and whatnot.  There is a world to explore and a place to write your thoughts down rather it is paper or on computer.  A diary is not a diary if you do not use it.  It is just a piece of paper or just a commuter.  Why do have a diary?  It is there when I need to write.  Not everyday do I write now-a-days but I write when I can and do have the time and need.