[dcb]

the problem I've had with leaving the ignition on is that it "stumbles", even on my multi-port saturn. So that I noticed a lot more accidental "relights" as you have to hold the kill switch in for longer, as the engine is stumbling along on a very non-stoich bit of fuel in a rather unpredictable manner.

It dies with authority if you kill the ignition
It doesn't inject another drop of fuel if you kill the injectors
So "ideally" you do both.

Also with the injectors stopped, you can add "forced DFCO" to your toolkit, once in a while it is handy to engine brake outside the pre-programmed DFCO parameters without using fuel.