what is the purpose of swaddle blankets?

I am slightly chlostrophobic and the thought of my arms being restrained makes me uncomfortable, i hate it. My mum said when I was a baby she could never wrap me up in anything even from newborn, because i would just cry until i could get my arms out. So the thought of putting my baby in a swaddle blanket where she wont be able to move her arms makes me uncomfortable and i wouldnt be able to do it. What is actually their purpose? It doesnt matter if I dont get any, does it?