Umm...three uses that I can think of:
1 - Deco. The plus side is, even if you don't lock it down it will never decay.
2 - Suicide. I do not recommend standing next to your axed pile of 124 blackrock and accidentally hitting your old Armageddon hotkey. I did that...once...
3 - And the (only) real use: Primeval Liche Champ spawn. If you are holding blackrock, you can attack wisps through those annoying shields.