Preliminary Bombardment is niche but has its uses. If the enemy army is taking cheap
MSU to the extreme it could be good value for only 2CP. If they're deep striking half their army and they've crammed the rest in to a handful of transports then not so much of course!
Orbital Bombardment is much riskier because of rolling the radius is affects, and it being reliant on your opponent bunching up units even then AND on your Warlord having line of sight AND not needing to move or shoot with your Warlord.