Planning source can be configured either for a particular project or all projects.
If needed, concurrency restrictions can be configured for a source. By default, concurrent events are allowed. User can configure a planning source in a way that concurrent events would not be allowed at all or concurrent events would not be allowed on assignee level. In addition, user can define issues as resources which will lead to concurrence blocking on issue level.
In case you would like to save some time when creating numerous planning events, you might want to set Default Summary to "As source name" or "As issue summary".