Mathematics for IGCSE & O level - Estimation (Section 3 - No. 21)
In which situation might estimation be the preferred method for a calculation?
When you want the most precise answer possible.
When you need a quick answer and precision is not critical.
When you are using a scientific calculator.
When the numbers involved are small and easy to work with.
Forklaring
When you just need a quick, approximate answer, estimation is best.