Boeing Mel
As any proper engine driver - not a modern diesel operator - knows, blowing off steam only achieves a reduction in excessive internal steam pressure; absolutely nothing else. It represents a massive waste of stored energy but prevents an explosion.
But that's a worthwhile purpose in itself for the blower-off.
There's less purpose in actually reading the blower-off's fulminations; even less in replying. The whole purpose, pressure-reduction, is achieved by the first post made by the blower-off.
So it's an entirely selfish act, enabled, I'm glad to say, by Prune.org.
Sometimes, we all try to entertain a bit, rather than blowing off steam, with mixed success. But that's another matter.