The Update Personalization Data job keeps the people returned by your personalization segment up to date and accurate. The job adds or removes people from the list based on whether they currently meet the conditions of the segment. If you ever need to check the current list of who meets the conditions of a segment, just click the ti ti-users button on the Personalization Segments page located at Admin Tools > CMS Configuration > Personalization Segments. The Update Personalization Data job updates this list. If you're curious about what's happening behind the scenes, what this job is actually doing is updating the PersonAliasPersonalization table. This table is very basic and acts as a link between the person (PersonAliasId) and the segment. The PersonalizationType field on this table has a value of "0" for all rows, which represents personalization segments. The PersonalizationEntityId field is simply the Id of the segment the person has been matched to.