It can be used for Life of unknown origin (as stated above by @mreith “The very base of the taxonomic tree” ) or is the result of IDs that are in conflicting Kingdoms
https://forum.inaturalist.org/t/state-of-matter-life-limbo/2870
https://forum.inaturalist.org/t/state-of-matter-life-clean-up/3556
https://forum.inaturalist.org/t/questions-unknown-v-state-of-matter-life/4080
Conflict can also show up often when a knowledgeable user types in the ID of the organism and the drop down menu gives several choices and the user accidentally selects a homonym that is eventually revealed to be a conflicting kingdom. Sometimes this happens with scientific name and sometimes it is a common name. Sometimes it is the original poster and sometimes it is later in the identification process.