Which is more useful, GDP or GDP (PPP)? Gross Domestic Product vs GDP Purchasing Price Parity?

Question

Is Gross Domestic Product by itself useful or is the GDP with the Purchasing Power Parity taken into account more useful?
I'm writting an essay about GDP
- China's GDP (standard) is around 4 trillion - however, China's GDP with PPP is 9 trillion.
What is the benefit of PPP, and which should I use?

Answer 1

Use both and explain what is the difference and how they are calculated.