Method 1 has one major advantage over method 2, method 1 only produces the desired product, C.
This means that as much as possible of the reactants is going into making the desired product.
We call this atom economy.
Method 2, produces an unwanted product, product F. This product maybe able to be sold for profit but is could be a waste product with little or no value. The other problem with method 2 is that, the desired product, C, will have to be separated from the unwanted product F. This means a separation plant will have to be build and this will incur a cost both financial and environmental.
The goal of any good chemist is to design a process where as little waste and undesired products as possible are obtained. This is not only good for the company finances but also the environment. Any waste products produced will have to be disposed of and this will incur costs both financial and environmental. Producing waste also uses up the natural resources and will produce pollution.
You can calculate the atom economy of a chemical reaction using the equation below: