We use LLD to dynamically discover ActiveMQ queues. After restarting the application these queues may not exist until they are used the first time. New queues may appear at any time as well as queues may disappear for ever.
This works quite well for items because they still get their values even if they are no longer discovered and if a queue is no longer available for a reasonable time it gets finally removed from Zabbix.
In this use case SLA calculation gets broken if it depends on triggers which are based on LLD prototypes.
Not sure if it's a bug or the documentation doesn't point it out clearly:
"Items (similarly, triggers and graphs) created by a low-level discovery rule [...] will be deleted automatically if a discovered entity [...] stops being discovered [...] they will be deleted after the days defined in the Keep lost resources period field pass."
That's exactly how it works for items but not for triggers.
Triggers based on LLD prototypes are deleted immediately if not discovered anymore. Normally that wouldn't have a big impact because they get created again as soon as they will re-discovered. But this behavior is really counterproductive if one got hundreds of LLD-Triggers that are used for SLA calculations in IT-Services.