LET allows you to assign names to intermediate values inside a formula. Its biggest benefit is often readability rather than raw performance.
Name the repeated idea
If a formula calculates the same rate, filtered range or lookup result several times, assign it once and reuse the name.
Debug one variable at a time
During development, temporarily return an intermediate LET variable instead of the final calculation. This exposes errors without dismantling the whole formula.
Use short, meaningful names
Names such as taxRate or filteredSales are more useful than x or temp when someone else inherits the workbook.