The original purpose of a coffee table seems so respectable and quaint. You and your spouse invite the Joneses over for dinner--presumably to show them you're keeping up with them--and afterwards, repair to the comfort of your living room, where coffee is served on a low table to "[encourage] conviviality and light conversation," as Wikipedia puts it. (Plus if the table's nice, you can disrespect your neighbor--who does he think he is, flaunting his yard like that--by demonstratively placing your feet on it.)
Then there's the coffee table book, a large, glossy tome sporting a design unconcerned with living a vertical life crammed on a shelf. It knows it will be able to sprawl out on the coffee table to entertain guests. It is the roomy suburban manse of the book world, unlike the Manhattan skyscraper shelf-hell that your other books live in.
An interesting piece in the Times looks at a darker coffee table world, one in which they are the instrument of child injury. The low table is the right height for your tot to slam into during play, and chances are you can recall several instances from childhood in which you or your playmates got a boo-boo from a Barcelona. Industrial designer Bruce Hannah, quoted in the article, jokingly refers to the Mies van der Rohe piece as "a deadly weapon."
Some might feel it's a furniture designer's responsibility to design coffee tables to be safe for all ages. Other would argue the burden is on the parents to child-proof their home or select appropriate furniture. But I prefer the sensible attitude expressed by one father in the article whose own child had a coffee table accident in someone else's living room:
"Life has hard edges," the father told [the apologetic hostess]. "Better he should learn it now than think everything's padded and be surprised later."