Documentation: Clarify "Update group memberships when logging in"

Starting in JIRA 7.3 we appear to have added this option in the external directory connector options: "Update group memberships when logging in"

Examples from the screens to add Crowd or LDAP directories below:

However Connection to an LDAP Directory and Connecting to Crowd or another JIRA application for user management do not appear to have documentation around this.

Please provide updates to explain this setting as when not used properly could lead to serious performance issues in Jira when using "Connector" LDAP type.