The weight located at or around the axis for vertical travel of the arm will keep the vertical effective mass and inertia low--good for tracking warps.
But, having that mass also well away from the arm to actually increase the effective mass in the horizontal direction of movement has its advocates. By increasing the horizontal mass, the arm will resist movement from the large displacement horizontal movement of the stylus in response to bass signals (deep bass is mostly recorded monophonically as horizontal modulation). In other words the arm resists moving side to side from deep bass modulation, so that most of that movement translates to lateral movement of the cantilever (i.e., more bass). This is the theory behind the Moerch Anisotropic arm. However, high effective mass in the horizontal plane of movement would cause problems with trying to play off-center records.
Other arms with low vertical mass but high horizontal mass include air bearing arms like the one on the Walker tables. It may be this design aspect, or something else, but I've heard great bass response from these types of arms.
But, having that mass also well away from the arm to actually increase the effective mass in the horizontal direction of movement has its advocates. By increasing the horizontal mass, the arm will resist movement from the large displacement horizontal movement of the stylus in response to bass signals (deep bass is mostly recorded monophonically as horizontal modulation). In other words the arm resists moving side to side from deep bass modulation, so that most of that movement translates to lateral movement of the cantilever (i.e., more bass). This is the theory behind the Moerch Anisotropic arm. However, high effective mass in the horizontal plane of movement would cause problems with trying to play off-center records.
Other arms with low vertical mass but high horizontal mass include air bearing arms like the one on the Walker tables. It may be this design aspect, or something else, but I've heard great bass response from these types of arms.