Digital Footprinting is an attempt to gain as much information about your company and / or employees as possible from publically available sources. The report at the end will highlight concerns such as pictures containing sensitive information like employee badges or operating system versions.
Also it might include company files that are current being shared publically. Due to configuration issues it is not unheard of that companies can accidentally publish sensitive files that are then indexed by Google or another search engine.
As such, it is highly recommended that this testing is performed regularly to ensure that no sensitive information belonging to the client or information that can be used to tailor an attack against the client is publicly accessible.