Often you will have multiple remote apps on heroku for one local app. Usually for different environments. For your app you might have a staging version and a product version. When this happens you have to use -a to specify commands to run.
A command will look like this:
heroku maintenance:on -a whirlwind-bird
It takes up memory remembering the names. Instead you can pass in the git remote name
heroku maintenance:on --stage staging