When members of a group specialize at tasks that would be normally be pursued by each individual separately, the aggregate task output of the group specializing at tasks will be greater than the task output of a group that chose not to specialize at tasks.
“Somebody not trained in pinking could probably only make one pin a day, and even when practised he would only be able to make twenty or so. Yet, dividing labour between pin-makers and non-pin-makers and by further dividing the task of pin manufacture between a number of specialist trades, we vastly increase the number of pins that can be made by each person. Ten people in a pin factory could and did, said Smith, produce 48,000 pins a day. To buy twenty pins from such a factor therefore costs only 1/240 of a man-day, whereas would have taken a purchaser a whole day at least to make them himself.
The reasons for this advantage, said Smith, lay in three chief consequences of the division of labour. By specializing in pin-making, the pin-maker improves his dexterity at pin-making through practice; he also saves the time that would otherwise be spent switching from task to task; and it pays him to invent, buy or use specialized machinery that speeds up that task” (42, The Origins of Virtue)
The Origins of Virtue by Matt Ridley