The no of cogs in the back makes little difference to the average rider. Beyond 7 cogs, its mostly about marketing. They do allow single tooth steps for time trials.
Triples were developed in the 1930s for touring cyclists, and are pretty much essential. A touring cyclists can find himself gunning along with a tailwind and a downhill, or having to haul a camping load up a steep, unsurfaced trail. The easiest way to achieve that range of gears is with a triple.
Im surprised that more people dont use 1x9 speeds, since you can get a considerable range for everyday road riding very simply. It is a popular system for cycle couriers.
Other less common systems are low-ratio doubles, as found in cyclo cross. These are good for non athletic road riders.
For just riding around town, carrying some shopping, it depends how hilly your town is. I've lived in places where a 1:1 ratio was essential.