It was a big issue during the beta, and apparently for some people now during the pre-patch. For me, it works fine now though.
Btw, Kill Command in Cataclysm isn’t strictly a BM ability, or otherwise strictly tied to a particular specialization. It’s a baseline class-wide ability. As for the specialization I’m playing, that being SV, it works fine. It’s just the pet commands and input that wasn’t working properly during the beta.
Kill Command in Cataclysm was reworked from the Wrath iteration. It’s now much more similar to the retail version, where you use it to deal some upfront damage to the enemy target when you use it.
Because it has such a low range(of use), only 5 yards, if you use it at any time when your pet isn’t within 5 yards of a target, it wouldn’t go off, nor would it cost you any Focus. It would only result in your pet starting to run towards the target you had acquired, when you pressed the ability. Do note that, if you use it when your pet is already attacking something else, and is within 5 yards of that enemy, Kill Command will be used on that enemy, and you will consume the Focus it costs.
I mostly used it to get my pet to attack an enemy I wanted to engage in combat. That said, Kill Command itself actually deals a fair bit of damage, even if you’re not BM, so it’s not a complete waste if it goes off.
In this case, it’s not that different. But since /petattack macros or other pet commands weren’t working much at all on the beta, this was essentially the only way to semi-reliably control your pet while leveling or doing other stuff in combat.
Again though, they seem to have fixed most of these issues now, going into the pre-patch, so no need to rely on Kill Command for this. Now, you can use macros, or keybind the buttons on your pet actionbar as normal.