Invisible Butt Joint
A butt joint in drywall will result in a raised layer of tape and mud because the edges aren't tapered. A good taper can minimize the ridge over a butt joint, but it's hard to eliminate it altogether. If you're installing drywall by yourself or installing in a space where it's impossible to deliver 12-ft. sheets, butt joints are going to be unavoidable. And if you're dealing with wall sconces or areas where raking light means a truly flat wall is imperative, a butt joint backer may be the answer.
A butt joint backer is basically a 4-ft.-long, 5- or 6-in.-wide board with 1/16-in. to 1/8-in. spacers added along the edges. You can purchase them at a drywall supply store or make your own. You could use an inexpensive 1x6 pine board and either glue or staple strips of ripped-down wood to the outside edges.
Installing the backer is easy. First, install the sheet of drywall, making sure the end doesn't land on a stud. Next, attach the butt joint backer to the back of that piece. Finally, fasten the second piece of drywall to the backer. When installed properly, the butt joint backer will cause the ends of each piece to suck in, resulting in a recess similar to the recess created by two tapered edges.