What is the point of summoning Boilers with Shadows of the Dead?

This is probably something that really, REALLY bothers me when I'm playing as Nekros against Infested, it's because boilers are considered to be a "high priority" unit, so instead of summoning charges, runners, you summon the elite units you killed, and that has boilers in the middle.

Boilers do absolutely nothing. They don't attack, they just stand around, drooling over their enemies. When the boiler shadow dies and summons more infested, they're enemies, not allies!

Boilers should be completely ignored by SotD. While I murder hundreds of ancients and mutalist MOAs - who are all quite useful in battle, instead of being just meat shields - I keep getting boilers.