My younger kids - and several of you - probably don't remember a time before the Internet...when the answers to questions, important and trivial, were a lot harder to come by. My father used to buy the new World Almanac every year, along with the Guinness Book of World Records - a practice I continued for many years. (He apparently had a problem with tossing the old Almanacs, because when I cleaned out the folks' house after my mother's death in the '90s, I found Almanacs going back to the late '50s in his library.) The Book of Lists and Leonard Maltin's books listing virtually every movie ever made were also great references.
I can remember the local library in the small Indiana town where I lived as a kid offered a service where you could call and they would look things up for you. In the '70s, I purchased a set of Collier's Encyclopedias, and always bought the annual Yearbook, which - in theory - kept the Encyclopedia current. When you bought the Encyclopedias, they gave you a paper containing a hundred little coupons, and if you had a question you couldn't find the answer to, you could write to Collier's, attaching one of the little coupons, and they would mail you some kind of answer - usually just photocopied newspaper articles, or something like that.
I'm sure that many formerly very useful and popular reference books are no longer even published. With the answers just a few mouse-clicks away, the need for them has largely gone away.