When dealing with upholstery, the materials are much thicker than your average entry point sewing machine will be able to handle. The feet might not be able to feed the heavy material through, and some machines will be physically unable to feed your material under the needle where seams meet. In most sewing projects there may be four or even six layers of material at some points where seams meet or need to be rolled over, which would require more space between the foot and plate than most machines could handle. So if your principle interest in sewing is upholstery, you will probably have to find a machine explicitly made for that task and it won’t be cheap.