They sure are handy for telling you which engine lights need attention immediately, and which ones can wait till next week/month. For those of use who are far from dealers, or too well acquainted with the rapacity of service depts, they're comforting in helping sort out the things we can do in the driveway from the bend-over-at-the-service-desk items. Also useful in seeing whether what you fixed was really the problem (see prior re "bend-over...").