because you might get mixed up
No
When the two numbers have an answer that is greater than or equal to ten.
yes u can if you need too
You might need to regroup more than once when performing multi-digit addition or subtraction, especially when the sum or difference of two numbers exceeds the place value of the column you are working in. For example, when adding numbers like 456 and 378, regrouping may be required in both the tens and hundreds columns. Similarly, when subtracting numbers like 804 and 297, regrouping may be necessary multiple times to ensure accurate results.
because sometimes the total is too big
When the squad leader deems it necessary to align, it means there is a need to regroup.
because 1 is toobig
15
only 2
No. It depends on how good you are at arithmetic.
159
It's not necessary, but it might be helpful because three is greater than one.