The only abuse I have seeing with the posting key happened a few weeks ago when a service used the posting key of every of its user to uptove their post.

But you are right, every key is important and the posting key used irresponsibly can cause bad things like spamming comments like crazy.

Either way, when you think about it, it was a genius idea to create several keys for certain activities. Now it looks obvious, but when designing the project I am sure it wasn't so easy to realize.

Cheers mate!