This matters. Although economies can grow nicely in the short-run by employing more people, in the longer-run, growth must come because employees produce more. This is what Paul Krugman meant when he famously said "productivity isn't everything, but in the long run it is almost everything." Slower productivity growth, if it persists, thus means slower potential output growth.
And this matters for investors. If the economy grows slowly over the long-run, then so too will earnings and dividends. Investors who buy equities in the hope of growth will therefore be disappointed. It's no accident that there is a decent correlation between productivity growth and the price-earnings ratio on the S&P 500; both were high in the late 60s, low in the 70s, peaked again in the late 90s, and have since fallen.