The 'Enable user session' tickbox on 'Advanced' tab of the Perforce credential caches the ticket and significantly decreases the number of 'p4 login' command issued by the plugin. This is very important to reduce contention on the P4TICKETS file and take load of very busy P4D servers. 

We should document this important feature in:

https://help.perforce.com/helix-core/integrations-plugins/p4jenkins/current/Content/P4Jenkins/credentials.html?Highlight=credential

Below is a screenshot of the feature.