Expired computers, computers that have not logged on recently, can be something you need to investigate. A client computer that has not logged on to the domain for, say, a month, could have been stolen. Such a computer could also be an under-used asset that is a candidate for redeployment. If it's a server that has not logged in for a month, it could indicate a computer that is non-functioning and one you should investigate.
This recipe is a variation on the Report on AD Users recipe.