However, you still have to get up and walk around to give your back a break from sitting. If your chair is worn out, or the table is too high or too low for you, your back will hurt. 6 - 7 hours of sewing is a long time to be sitting - it takes a toll on the body.
My sewing area is set up so I must get up and walk to the ironing board or cutting table. If I don't do that, I am in deep trouble pain wise.