Measurement aside, there are two reasons aggregate growth might matter. The first is to create jobs to assimilate the unemployed and anticipate increases in population. The second is to improve living standards. Economic logic does not require overall expansion to achieve either of these objectives. An expanding labour force can be accommodated if hours of work fall. And it's productivity growth, rather than the overall size of the economy, that drives improvements in living standards. Getting bigger doesn't necessarily yield wealth; improving productivity does.