The coffee table is an ingenious device that serves many purposes in today's busy world.
Firstly, it acts as an overflow platform for the bit of kitchen surface next to the sink. Dirty plates, mugs, cutlery and occasionally magazines mingle gregariously with empty bottles and food wrappings. The space beside the sink is usually high up, so items falling from it are at risk of breakage. The coffee table on the other hand seldom rises more than a foot from the ground. Plates can be stacked endlessly with no risk of damage should their stacking become too precarious.
Secondly, the coffee table is a far more comfortable thing on which to rest one's feet whilst watching television than anything designed for such a purpose. Very few people actually buy pouffes or ottomans (or whatever they're called) because the coffee table is much less expensive, may be wiped clean and can support a great many feet along its length.
Thirdly, most coffee tables have a small rack beneath the main surface on which newspapers, magazines, television guides and remote controls may be hidden.
Not only do coffee tables function as a repository for many belongings1, they are also the source of a calming and skill-developing pastime: the art of rearranging the plethora of junk on the table's surface. Despite the surface clutter - every mug in the house, the plates from three weeks of meals and newspapers no-one can remember buying - room can always be found by the skilled rearranger for their feet. This means that when they get up to leave, the plate, glass and crisp packets the table user has generated during their stay will have somewhere to go - they can simply be transferred from the chair-arm or the floor to the space on the table from which feet have recently been removed.
Marvellous things, coffee tables.