- UIs that want minimal visual thrashing in "user time" (wall clock time)

- Databases and B-Trees and other storage with primary key indexes/clusters that offer slightly better writes/clustering for "roughly but not necessarily exactly in order insertions": key/value stores, document databases, SQL databases

Wall clock time is plenty of time for a UI to rely on a partial ordering.

Databases are generally designed for arbitrary order insertions, it's just common that they are most optimized/efficient for "roughly in-order". A partial order is generally good enough to opt-in to most of the optimizations/efficiencies and reduce worst cases, especially if the "out-of-order" insertions occur below wall clock time and things like journaling-based transaction semantics versus competing with clustered inserts, reindexing scanners/services, and so forth.