Yes, get rid of those pesky selvages. They have a different density than the body of the fabric and will give you major problems later. I snip and tear the narrowest possible selvage, (doing a very small sample first, as some fabrics don't tear nicely.) but at the last minute, so they won't have loose threads to get in my way. For very large quilts, however, I often prefer to buy extra large backing fabrics. I sometimes buy them on sales at very low prices.