Only occasionally. My errand bike/dog taxi has a Dutch AXA frame lock. Kinda like a car's ignition key: insert key--rolls. Remove key--stops.
Someone can still easily pick up my beloved dog taxi and throw it in the back of a pickup, but the only time I'm ever far from my bikes are when I'm riding one of the other ones. My other bikes are protected only by a bloodthirsty psychopath with two strikes (so far) and nothing left to lose.
And to answer your specific hypothetical, I never completely finish when taking a restroom break. I always save an eager residual for the unconscious thief who tried. You know those survivalism
enthusiasts who can't wait for the worst to happen? That's how I am about my bikes being stolen.