A customer has just called you up complaining that you did an inferior job repairing their bathroom. The work you did a year ago isn’t working. You don’t remember the job in detail so to appease them you agree to fix it for free. After you arrive it comes back to you though, you didn’t do work on this bathroom but you did recommend that work should be done. It is too late however you agreed to do the work for free, and they are insisting. An easily available customer history that includes work completed as well as recommendations that were made could have easily diffused the situation as well as shown your client how well you remember them.
Customer history additionally benefits inventory. When you know beforehand that a client has metric instead of standard piping in their home you can bring the appropriate materials along in addition to the normal load listed above saving another trip. It can also be useful for a client you needs to know what work you did last year because they are now selling the house.