The CGI companies have and use huge render farms...  Some of these backdrop people don't need real faces nor legs... If there are obstructions in the scene and all you see are mid sections.. then that's all that is rendered...

Sometimes It is safer and cheaper -(insurance wise)-  to have 10 to 15 mesh -- interacting--  characters pretending to be pedestrians than to have real people waiting on the side lines..   They often re-shoot over and over again the same scenes that did not work right..  sometimes due to safety health concerns..      time on the field is money... 

But  this is not what this company has in mind... they are concern about Video games...

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