Premium economy is easiest to justify when the flight is long enough to make comfort matter but short enough that business class pricing feels silly. On a five-hour route, the value comes down to sleep, schedule, and what the ticket includes beyond the seat.
Where it helps
The extra recline and legroom are most useful on evening departures, early arrivals, and routes where you need to work or drive after landing. If the fare includes checked bags or priority boarding, compare the full trip cost rather than the seat cost alone.
Where it does not
For a midday leisure flight with a good exit-row seat available, premium economy may not change the trip enough to justify a big jump. Spend the difference on a better hotel location instead.
Simple rule
If premium economy is less than 30 percent more than economy and the schedule is rough, it is worth a serious look.