Yes, classification of economic activities into primary, secondary and tertiary sector is useful as it helps in estimating the relative importance in the growth in GDP of the economy. Classifying in such a way helps in calculating how much goods and services are produced and how many people work in each sector. In India tertiary is growing at a very fast speed which implies that the country is moving towards developed country. This type of classification helps in comparing the level of growth in different countries.
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