What does path.conf do

I am new to elastic search and was confused what path.conf exactly does. I saw another question on this but it didn't seem detailed enough.

I understand how the path can be specified at launch via a flag, I was unsure what the field in the elasticsearch.yml file does and why it is necessary if the path of the config files is different

A detailed answer here would be very helpful and much appreciated. Thanks!

It's useful if you have multiple, custom path.whatever values, so you can run ES with bin/elasticsearch -Des.config=/path/to/blah and then have it pick these up without having to define them on the CLI.