Timelines can teach you so much about - well, obviously - what happened when in a particular family. But they also do much, much more...
They provide a way to discover a family's migration pattern. For my family, all roads lead to Washington state. Major emigrations have resulted in quite a few family members in the Tacoma area, the Vancouver/Portland area, and of course, Walla Walla (I'm convinced we own half of Mountain View Cemetery). Going back a few generations, it's interesting to see how everyone ended up there and all the different places they came from.
They allow you to see how one major life event affected the rest of the family, such as the early death of a husband and father; how national and world events, like the influenza epidemic of 1918 and World Wars I and II, change ancestors' lives; and how such things as abuse, alcoholism, and divorce can continue through many generations.
They give some insight into where those "lost" relatives might be hiding; the siblings and cousins who were alive at the same time; which mothers were around when their daughters were married, and which daughters went wedding dress-buying on their own; which fathers carried more of the "girl" chromosome or the "boy" chromosome. The Keen family men are noteworthy - Grandpa Keen had four sons and two daughters, but of the three sons who survived to adulthood, two sons' children numbered eleven, and out of those, ten were girls.
For these reasons and others, I enjoy creating and studying family timelines.
Below are some timelines I've put together for my great-great grandparents. The names of the living have been omitted.