Time-ordered IDs for modern schemas
Random UUID v4 spreads inserts across index leaf pages, which can fragment storage on high-write tables. v6/v7 trade a little predictability for locality—often worth it in event logs and ledger rows.
Clock dependency
Timestamp components reflect generator clock time. NTP drift across nodes is usually minor, but never use client-generated ordered UUIDs as sole proof of event ordering in distributed audits.
Interop with string APIs
Most services accept canonical 8-4-4-4-12 lowercase hex with hyphens. Store consistently—mixing uppercase in URLs can break case-sensitive caches.