What is the primary scientific benefit of using astrometry over transit or radial velocity methods?

It allows astronomers to solve directly for the inclination angle ($i$) to find the true mass

The radial velocity and transit methods are inclination-dependent, generally yielding only a lower limit on mass ($M \sin i$) because the measured signal is diminished if the orbit is not edge-on ($i e 90^ ext{o}$). Astrometry's unique advantage is that it measures the angular separation and positional change directly in the plane of the sky. By combining this positional data with the star's radial velocity (obtained spectroscopically), astronomers can solve the system geometry to find the inclination angle directly. Once inclination is known, the mass derived from the radial velocity signal can be converted into the planet's unambiguous true mass, which is vital for determining density and composition.