I've never used them, but have seen traps set up that way so assumed that was what he was talking about. Probably would work better to hold coons than a regular offset. Some states require an offset, so that may be his reason. Old time trappers using sharp jawed traps first went to offsets to avoid cutting ligaments. Nowadays with most traps either not having sharp jaws or trappers knowing to file sharp edges, that is not such an issue.