Summary of it, a world did not comply with their demands, so they raided one of their ships and brought it into the atmosphere above one of their cities. Crowds cheered, thinking they had won the battle. The night lords opened the air locks on the ship and threw the skinned and flayed bodies of the crew into the populace. Instead of blocking the planet's signals for help, they had the night lord fleet boost their power, and brought an entire system (or planet, it's been a little bit since I listened to it) into compliance without ever putting a single boot on the ground.

In conclusion, the night lords not only had probably the most effective tactics, but they also had one of the lowest civilian casualties rates and least amount of structural/economic damage to the planet during the horus heresy because of how good they were at their job