The difference is you add it as an afterthought whereas it's the first investigative action in the procedures. It shows clearly the reason electrical equipment must be able to be electrically isolate individually and therefore addresses the original point.
When/if I have smoke in the flight deck, I'm going to know right away which system is offending? You sure about that?
I'm going far, far out on a limb here and pretty much say that unless it's clear it's a coffee maker, oven, or something not in the FD, I'm not going to have time, nor want to waste time analyzing which system it is, then waste more time considering how to do that ("where is that darn VHF3 circuit breaker again?!"). Rather, I'm going to depower busses PER THE CHECKLIST, and wait to see if smoke decreases or not. All the while running toward the ERA or nearest airport.
To add to my point, an airplane like a 777 has avionics in the bay. Most panels in the flight deck are merely control heads. To try and determine from which LRU/bussbar the smoke is emanating is virtually impossible.