Yes, classification of economic activities into primary, secondary and tertiary sector is useful as there are varieties of economic activities that are performed by the humans. In order to understand the nature of these activities and the role performed by the people in fulfilling these activities we need to classify these into the three sectors.
Further, the classification also helps us in ascertaining the contribution of each sector to the Indian economy. The government on these bases may also initiate reforms in a sector which according to it had not developed up to its full potential.
It also 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 sector 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.