Use when emoji or Unicode characters fail to store, "Illegal mix of collations" errors appear in JOINs, ALTER TABLE CONVERT TO is risky, or migrating charset from latin1/utf8mb3 to utf8mb4. Prevents the common mistake of using utf8 (3-byte alias for utf8mb3) instead of utf8mb4, mixed-collation JOIN
Use when emoji or Unicode characters fail to store, "Illegal mix of collations" errors appear in JOINs, ALTER TABLE CONVERT TO is risky, or migrating charset from latin1/utf8mb3 to utf8mb4. Prevents the common mistake of using utf8 (3-byte alias for utf8mb3) instead of utf8mb4, mixed-collation JOIN failures, or in-place CONVERT TO breaking index-prefix limits. Covers utf8 vs utf8mb4 (3-byte trap),