I lost my father when I was 22 and my mother about 7 years ago. I consider myself very lucky that my father felt compelled to write his memoirs and that I have kept many years' worth of my mother's correspondence. Being able to go back and read these materials from time to time keeps their voices alive.
What people whose parents or loved ones are living don't always realize is the complete and total finality of the exchange when a person dies. Whatever questions you wanted answered, whatever stories you loved to hear, whatever connection you had is over. The beauty of personal history is that it helps loss be minimized.
Personal history is the term I use for any work that preserves a connection with family. Some people like to see the family laid out in an extensive family tree, others want a tribute book to honor a loved one and share that person's stories with new generations. Others simply want to capture a special time, such as the experience of immigrants or soldiers. This can be done in writing, in the form of books or photo books, or through an oral history interview.
These are all wonderful ways to provide a meaningful connection and gift for future generations. They may not know it yet, but today's teenage grandchildren will one day tell stories to their kids about their childhood. Imagine how much richer that conversation can be when a memory book is available to show pictures and remember individuals with clarity and love.
Whatever the subject, don't do yourself the disservice of thinking family history projects are frivolous or self-indulgent. A well conducted family history book can be one of the most significant items you leave your family.