It's helpful because let's say you have $3.23 and you need to give someone $1.00 then you would need to subtract then what way you will know what you need to do and how many money u have left
Its a lot easier to do 1.200 - .200. Than to do 1.248- .239. How I see it, estimating always gives you something to fall back on or to help see if your exact answer is accurate
