If the wall is acceptably straight, looks okay, and doesn't have any cracks or marks from old water damage or similar issues, there's no reason to do more than just spackling and painting.
However, if the walls are made of something like Tretex material (which is a porous form of wood fiberboard) and perhaps have been wallpapered a few times and have a crack in a seam, the quickest and simplest solution is often to put up renovation plasterboard. This will give you a good base to work from.