I still cringe every time I think about having to ask for it again and how much trouble it must be for an author to do that over and over for people like me who didn't take the time to save it in the first place. I have found myself referring back to that binder time and again. This is not to say that it is not convenient and helpful to have all that information saved somewhere on your hard drive because it is. I recommend though that you don't totally rely on your computer as a single back up source. It is also important to make back-up copies of important data kept on your computer.
Any financial information comes quickly to mind.
Many people today keep their bank records on computer. There are also a lot of people who use tax programs. Even treasured photos should probably be backed up. I went to visit my dentist today and, while I was there, heard her discussing with office staff the severe dilemma they were facing because of a crashed hard drive. First of all, they use computers from the Dark Side, and if theirs crashes as frequently as the one I use at work I feel for them.