A valid, up-to-date and accurate counting of our systems is one of the underlying building blocks that are absolutely necessary in having a successful security program. An inventory has a half-life, a certain amount of time between when its created and when half of the information it contains is superseded. Even people with the best of intentions often forget about one or two systems that have been used by the department since time immemorial. ByOD/IoT and the Cloud brings its own set of problems for inventories.”]
Source: https://securityintelligence.com/start-2015-right-take-inventory/