why is wait group necessary in streaming post request to elasticsearch

[Alexander Mills]

I am trying to figure out why the wg is seemingly necessary as part of this code to stream JSON to a post request to ElasticSearch:

https://gist.github.com/ORESoftware/06341057ca39e1b2a47dc8a8e4e4b55f

Any tips appreciated. If the waitgroup is not used, it doesn't appear to wait until the full request body is received? Not sure.