I did sew up a number of my sweaters on the sewing machine many years ago. It did work and it did allow me to wear these sweaters after spending all that time knitting them. I was never happy with how they looked being hand sewn with yarn. That said I have learned a lot about finishing techniques with the internet as well as all the possiblilities of knitting in the round with no seams ( I love that!). I agree with Ingrid, with the newer snugger styles especially the lack of stretch in the seams would be much more noticable than they were in the 80's with the oversized baggy sweaters I was making.
I am in the process of dissassembling some of those sweaters so I can reuse the yarn to make more stylish and form fitting clothing.