This number is useful to recall, first because it can be used in to judge relative country sizes if you happen to come across another country's GDP figure. Also, the number will be useful in comparison with US GDP in the future. That percentage is relatively constant over time, even as the economy moves between recessions and boom times. Also notice that services is the largest sub-category in consumption. This category includes health care, insurance, transportation, entertainment, etc.
Investment represents how much the country is adding to the capital stock.
Since capital is an input into production, the more capital equipment available, the greater will be national output. Thus, investment spending is viewed as an indicator of future GDP growth. Perhaps, the higher is investment, the faster the economy will grow in the future. One concern about the US investment level is that as a percentage of GDP, it is lower than in many countries in Europe and especially in Japan. There was a fear amongst some observers, especially in the 1980s and early 90s, that lower US investment, relative to the rest of the world, would ultimately lead to slowber growth.