Activate this option to convert geometry used for deforming objects into real bones in the FBX file.
3ds Max lets you use geometry to deform other geometry (as would bones), but other applications do not support this kind of deformation.
Use this option to keep deformations but convert geometry used as bones into actual bone objects.
In earlier versions of Maya, you could not use geometry to deform other objects instead of bones. This option lets users import objects from other software that had a Use Geometry as Bone option, such as 3ds Max and Softimage into Maya.
For example, if you had a scene in 3ds Max where a box was used to deform another box, the geometry as bone object became a proper bone object in Maya if the Convert Geometry used as Bones option was active. If you disabled this option, the box would remain a box and there would be no animation.
Maya now supports this type of deformation, so it is no longer necessary to activate this option. However, it is still a best practice to leave this option activated for improved interoperability as not all products support geometry as bones.