Zeroing the figure in the Joint Editor only zeros the rotations, it has no effect on translations.

You would think that an un-scaled figure with IK off, and with all its rotations and translations zeroed, should end up standing on the GROUND plain. Offten this is not the case. Many zeroed fiures will have their feet slightly below the ground (see graphic above).

Some other facts to consider.

The figures default pose, that is to say the pose it loads in, and the pose it will normally adopt if 'Restore Figure' is used (so long as this has not been reset), is usually not the same as the zeroed pose. The figure may be standing on the groung in the default pose, but zeroing the figure may put its feet below the ground.   

To empirically determin the zero elevation for a figure in some particular pose, you can use the Right or Left Camera, and set the GROUND to Wireframe Display style to give a datum line. 'Drop to Floor' works well in most circumstances, but there are two more factors to be concidered. The Poser GROUND plain is NOT at zero elivation, it is actually at -0.001 Poser Units. The feet may not look the best when they are technically at zero elevation, feet squash when weight is put on them, and they will also sink into a soft surface like a carpet. For these reasons, the figure may look more natural if yTran of the hip is 0.004 to 0.006 Poser Units below the position when Drop to Floor is used.

A pose to inject morphs should in general NOT change any translations or rotations, the end user may already have set the pose, and probably does not want it tampered with.