What does it mean if there is no delegation in a Certificate?

Kinda, althought that’s confusing terminology, given that there is the “Blackhole canister”, so I’d consider a “blackholed canister” on that has the Blackhole canister as the sole controller.

What’s the benefit of leaving the blackhole canister as the controller as compared to removing all controllers?

It allows anyone to call canister_status, e.g. to get the cycle balance, which otherwise wouldn’t be possible. This enables applications like the the cycle tip jar.

Also, following up my initial question, what does it mean if there is no module_hash for a canister?

That the canister

  • has been created, but no code installed yet, or
  • had code installed, but it got explicitly removed (via uninstall_code),
  • it ran out of cycles, and got emptied by the system.