There are few of reasons the recommended way to do walls is to go horizontal with the sheets. First is the straight edge is against the ceiling which gets done first, this holds up the edges of the ceiling and covers the cut edges of the ceiling. Second going horizontal makes for less joints to tape. Third starting at the top puts the cut edge of the wall at the bottom were it gets covered with trim. Also the pros use longer sheets 10', 12' 14' or 16' to reduce end joints which are not tapered for easy finishing.