When installing a rigid pipe in a trench, why is haunching (compacted fill from the bedding up to the springline) so important?

1. Haunching is only cosmetic and may be left uncompacted if the invert is on grade
2. Well-placed haunch support carries a large share of the pipe load; voids at the haunches let the pipe settle, rack, or crack
3. Haunching replaces the need for any bedding under the invert
4. Haunching is required only for corrugated metal pipe and never for concrete pipe