East Coast professionals working with West Coast partners check this conversion constantly. Sales teams in New York calling prospects in San Francisco, or product managers in Boston syncing with engineers in Seattle, need to avoid early-morning disruptions on the Pacific side.
Eastern Time is 3 hours ahead of Pacific. A 9 AM call in New York is 6 AM in Los Angeles — far too early for most. End-of-day on the East Coast at 5 PM translates to 2 PM Pacific, leaving plenty of West Coast afternoon remaining.
Because both zones follow the same US Daylight Saving Time schedule, the 3-hour difference never shifts. There is no period of the year where the gap becomes 2 or 4 hours.