Why do we need to separate different components of a mixture
Many substances are not pure and exist as mixtures, with impurities present along with the required substance. Different components of a mixture are separated in order to either separate the un-required components from a mixture or sometimes, to separate more than one useful components from a mixture.
For example, grain purchased from shops can contain several impurities such as pieces of stone, husk, broken grains, etc. Thus, grain is separated from these impurities to make it edible.
Similarly, after preparing tea, we strain it to remove the used tea leaves from tea.