Why is it always necessary to maximize yield in a chemical reaction?
Supposing you were baking a cake, and your flour, sugar, milk, eggs, and butter had a mass that totalled 1 kg. The cake came out of the oven and its mass was 995 g - clearly you left some of the cake batter in the basin, when you transferred it to the baking tray, but you would not expect to get a mass of over 1000 g.
Now, mass is conserved in any chemical reaction (while it is not conserved in any nuclear reaction), however, our ability to scrape out the product from the reaction vessel is necessarily imperfect. Then too, the reaction might not even proceed with 100% yield. Purification steps, such as recrystallization, will also diminish yield. Natural product chemists, who design and implement multi-step organic syntheses, typically start with kilograms and finish with milligram quantities, as each step of the total synthesis is less than 100% yield. Even with 90% yields at each step (and a chemist would be very happy with such yields) it would not take too many steps before your products become smaller and harder to isolate and handle.