Never
Just because you're at a wifi hotspot like a StarBucks doesn't mean you're actually connecting to the StarBucks network (even if the network name is StarBucks Guest or whatever). It is easy enough to place a portable hotspot in the same area, give it the same name as the legit one, and just skim all traffic.
Having said that, there is no such thing as security anywhere, at anytime; not your home hard-wired and definitely not a public hotspot.