For Example
I required Total quantity for my project = 1000 cum
i actually consume = 1028 cum
so i over-consumed 28 cum, but if i check it % in total quantity i.e. - 28/1000 it comes to 2.8%
If my company standards allows me a difference up to 3%, then during reconciliation i can say the difference is in within limit, this saves Ass of engineer and contractor
So you already have a bigger wastage factor than steel volume, that is the reason its not even consider.