It has been used as a way to carry swords; in these cases, the sword would have been unslung from the back/shoulder before being drawn. Some examples:
Republican Chinese soldier with dadao: https://i.pinimg.com/originals/b8/cf/fb/b8cffb96e2e83cb3f92781f751dddb1e.jpg
Samurai with odachi: https://commons.wikimedia.org/wiki/File:Hiyoshimaru_meets_Koroku_on_Yahagibashi,_showing_nodachi_or_odachi.jpg
Samurai with odachi: https://commons.wikimedia.org/wiki/File:Samurai_wearing_a_nodachi_%28field_sword%29.png
It works as a way to carry long objects, as seen by other weapons being carried slung over the shoulder or across the back:
Rile: https://commons.wikimedia.org/wiki/File:81_m-m_Mortar_crew_in_action_at_Camp_Carson,Colorado-NARA-_197171.jpg
Lance: https://i.pinimg.com/564x/f9/ef/b4/f9efb4b3f8a5abf13274ebdf98f7eee3.jpg (over the arm, rather than the shoulder, with the butt supported at the stirrup)
There are some examples of swords being worn at the back, at the waist, keeping the out of the way, but still allowing them to be drawn:
Qin charioteer: https://commons.wikimedia.org/wiki/File:Qin_charioteer_with_back_scabbard.png
Celtic: https://i.imgur.com/0zj5FJX.png (see https://doi.org/10.1017/S0003581500022460 for more info on these)
Gurkha with kukri: http://3.bp.blogspot.com/_k07pirzBU34/TUKc_C1KuTI/AAAAAAAAGwU/LCucApGc8Q4/s1600/Gurkha_IOC_3.jpg
