Dilution techniques provide simple and accurate procedures to: 1) change the concentration of a solution; 2) indirectly "weigh" a solute whose weight is significantly below the usual limits of analytical balances; and 3) determine the quantity of bacteria in a culture.
4)Dilution is necessary for getting isolated colonies, from which pure culture shall be obtained
5)if a sample is plated without dilution, then there wont be any isolated colonies. So dilution is necessary for getting isolated colonies, from which pure culture shall be obtained.