I find this one way of doing things very odd. When you're younger and at school you think everybody does it the same way. You hit university and you realise even those who are interested in or very good at the same subject do things differently, that teachers can be so wrong on maths it's unreal. I remember a particularly illuminating tutorial when the Head of Department was asking about how people see and learn things. He was still interested in that after 35 years.
The only reason to do linear sums surely should be to save space on the paper. Other than that I shouldn't think it matters at all. To berate people seems childish, it is not in the spirit of maths at all.