When a user visits your Site, SiteSpect determines which Campaigns that user is assigned to depending on Campaign Set, Campaign Overlay settings, Audience, Eligibility Sequence, and Traffic Split/Frequency.
SiteSpect may assign one user to multiple Campaigns at the same time, but to only a single Variation Group in each Campaign and never the same Campaign again.
You can configure the length of time a user is assigned to a Campaign with the Advanced Settings by modifying the Assignment Expires After thresholds for Visits, Duration or Previous Visit Gap.
Users who are not counted when assigned to a Campaign are then unassigned and are eligible for to be reassigned to the Campaign on their next visit as long as they still meet the conditions.
An assigned visit is a visit during which the user is assigned to at least one Campaign. Sites with several active Campaigns typically have a low number of unassigned visits.
In addition, if a user fails to be included in the Audience for a Campaign during one visit, the same user may be assigned to the same Campaign if the user later meets the Audience requirements.
Some useful Visualizations on this topic can be found below: