Good habit to hit the kill switch, so you don't have to think about it or find it if you ever need to.
I disagree about it being a holdover from the old days. Sticking cables and carbuerators might no longer be an issue, but the bikes are more complex than ever, and computers fail in strange ways.
My 08 SEUC had a bad cruise control switch. I was on a rural road doing about 60mph when the cruise engaged all by itself and started accellerating. I immediately hit the kill switch and pulled in on the clutch. As the bike slowed, i thought for a couple of seconds, disengaged the cruise switch on the fairing, turned the kill switch back on, and kept on cruising.
Use the kill switch.
And turn the cruise control off if you're not actually using it at the time.