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 value lost to inflation. It is the true value of your money. It is your true loss or 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 you your actual gains, the actual buying power after considering inflation. Look at it and decide how much your buying power grew.
Gray line: This line lies. It tells you the absolute amount of money. It doesn't tell the actual buying power after considering inflation.