Why use this tool? Because it clearly tells if your buying power is increasing or decreasing.
Just look at the green line. The green line tells you the buying power in future, after subtracting buying power lost to inflation. It is the true value of your money. It is your true gains.
You shouldn't really care if 1000 is becoming 5000 after 5 years. You should care if the buying power is increasing or decreasing.
Green line: This line is the truth. It tells the actual buying power of the 5,000 after you deal with inflation.
Gray line: This line lies. It tells how much your money grew, the number. It doesn't tell how much your buying power grew (despite inflation).Your gray line may look like it is going up, but because of inflation, you might still be in loss.