Every time I travel by train during working hours, I get reminded of the old “shoulder surfing” attack; a surprising number of people are working away on their laptops seeming unaware that anyone peaking over their shoulders has a good chance of catching what they are doing.
Which is all very well if it is something innocuous, but what if the work involves sensitive information?
It may seem unlikely that any serious compromise could take place in such a way, but it has been known to happen. Besides it’s a good excuse to put away the laptop and get on with something more fun.