Use when date/time behavior depends on timezone, DST, date-only parsing, floating local inputs, SSR/server zone differences, or instant-vs-wall-clock boundaries — wall-clock values stored with no zone, `new Date("2026-06-14")` parsed as UTC and printing the previous day, `datetime-local input` floating values with no zone, adding 24h across a DST boundary, or `toLocaleString` rendering the server's zone.
