This script creates raport of custom fields usage: connects custom field with project. If there is at least one issue in project which has value in particular custom field, connection is created. Please mind the projectRatio=0.1. This argument means that custom field which is used in more than 10% (0.1) of projects will not be placed in the list (chances for creating project context for such custom field are low).
Should be used from ScriptRunner plugin running in JIRA.