I notice some versions of Wing Chun do the bent back version of the elbow movement in the third form or Biu Gee form. I know Wang Kiu's lineage did this, Pan Nam's lineage does this and today I noticed Wong Shun Leung's lineage via Nino Bernardo do this. The vertical people have one interpretation of these movements and the bent back people have another. I think both could be argued. For me I now prefer the straight version especially since I have had a some back problems in the past and during those times I couldn't do the bent version. Also for the much smaller person I think the straight version may be better. I see some usefulness in the bent version is various throwing applications and to get the idea of more body movement freedom. But artistically I like the look of the straight approach better.
http://www.teamwingchun.co.uk/wingchun/forms/3rd.htm
So I am wondering what other lineages out there do the bent version? Maybe check the link to understand what I am talking about or see Pan Nam's third form on his video.