When you are using LLD e.g. for monitoring Powersupplies you maybe get a Problem if a Powersupply fails.
The next LLD-Discovery-Cycle maybe didn´t find that Item again and therefore the Trigger will be deleted and the Trigger Notification as well. So, when e.g. a Powersupply fails during Weekend and the LLD-Discovery is running at Weekend you will not recognise it on Monday, because the Trigger and the Trigger-Status are deleted.
I think the "keep lost ressource period" should be used for the Triggers just as Items. So, the Trigger-Status will be available during this period.