What is XIRR?
Extended Internal Rate of Return (XIRR) calculates the annualized return for a series of cash flows that occur at irregular intervals (unlike CAGR which only looks at start and end).
When to use XIRR?
XIRR is necessary for SIPs (Systematic Investment Plans) or any scenario where you buy and sell at multiple different dates. CAGR is incorrect for SIPs because not all money was invested for the full duration.