Why should fossil fuels not be wasted?

We are well aware of the fact that Fossil fuels take millions of years to form under certain atmospheric conditions. Fossil fuels are the non renewable sources of energy that once after the depletion cannot be restored. As they are necessary for the industrial and household uses, worst is predicted if we will have to face their scarcity. To sustain these fuels and to avail the future generations with the same, they should be used very carefully.