Why not just teach kids to do addition so they get the right answer. Then they don’t have to worry about estimating the number, they know what it actually is.
1. Many real life problems don't require exact answers.
2. Most people (even students now, unfortunately) will use calculators for the exact answer. Estimates are good to check for fat fingering the inputs so you know the answer is way off and needs to be redone.
3. Long multiplication and division require many steps where it is very easy to screw up and put the numbers in the wrong columns. Estimation gives you a quick check to make sure you haven't really screwed up.
4. In long division to get each individual digit of the quotient you make an estimate of the current division. For example 63496/874 will be estimated to be 70 (63000 / 900), which will give 7 as the first digit of the quotient.
I was gonna say......if they just teach them basic arithmetic they don’t have to estimate. lol