– Larger mass slows down acceleration (not for gravity where the motion is constant regardless of mass!).
– Larger mass means larger inertia, so also braking a soft body is more difficult.
– Do not confuse Gravity and Weight (both measured in Newtons) with Mass (measured in Kilograms)!

– In this example a Wind Force Field (the arrow) is moving a soft body. The bigger the mass the smaller the displacement.

Blender Soft Body Object Mass