Sculpting and detail painting are two-handed jobs, which leaves nothing to hold the part. A holder solves that: an adjustable grip you can turn and tilt, either hand-held or mounted on a weighted stand, that keeps the piece at a working angle and away from your fingers. The benefit is not only comfort — a part that cannot shift is a part you can put a fine line on.
A hand-held holder suits figures you want to rotate constantly; a stand-mounted version frees both hands and is better for sculpting, where you push against the piece. Check the jaw opening against what you actually build. The wider range of stands and clips holds sub-assemblies while glue cures, blades and styluses are in sculpting tools, and the branch overview is in sculpting tools and materials.