Lets say you have got a production app running on Heroku. Most likely you have got another staging app where you conduct all your experiments before pushing you code to production.
Now every time you want to run a
heroku command specifying app name can get annoying quickly, instead you can choose run the following command after which Heroku will set app associated with the remote as your default app for running all your Heroku commands.
git config heroku.remote staging
Assumption: remote for your default app is