With addition, you need to regroup in the event that there are more than 10 ones or 10 tens. In a subtraction, you must regroup whenever there are insufficient ones or tens to subtract.
1 tens and 2 0nes
When the squad leader deems it necessary to align, it means there is a need to regroup.
500+10+6 = 516
78 can be regrouped into 6 tens and 18 ones.