Use of proxy setting

I noticed the following proxy-related commands while setting up my local env;

npm config set proxy
npm config set https-proxy

I am not sure what is it really useful for? Please suggest.

Sets the proxy to use when fetching things (i.e. packages) over the network.

So does it mean it will be used for every HTTP request…

even when I am testing locally an API of the form http://localhost:4200/api/someFiles

No - it only affects npm commands. Your Ember server is not part of npm.

Oh so does not affect running my test application in browser …

ember serve --proxy http://some-other-url

for one off proxying

or ember g http-proxy /api/v1

for sticky proxies