What is the purpose of #haltIf: aBlock?

Right now, you can pass any of the following to Object>>haltIf:
  - aBlock taking an optional argument which is automatically set to the receiver of #halt
  - aSelector which looks up the call chain and halts if present
  - aBoolean

So, whatever the condition is, it seems like you should be able to evaluate it in the calling context. When would you ever need to use a block? Can we eliminate the block behavior? Or, who has a great war story about blocks saving them from imminent doom...

Thx.
Sean