The psychological effects of a smile are too many to mention. Researchers know this. Mothers know this. Friends know this.
The effects of touch on human behaviour are studied similarly well. Waiters and waitresses know this. Psychologists know this.
Does this mean that all our interactions need to be smiley-touchy-feely all the time? No, of course not. Any sort of interaction can be unwarranted and unwelcome, including these.
But on the whole, every time we give a machine a chance to do a pie...