Dependency manager like bower and npm support a neat feature to add dependencies to your project via the command line. So if you want to install lets say "jquery" via bower, you don't have to manually add "jquery" to your dependency file, you simply have to enter bower install jquery --save and the "--save" option puts the dependency in your project file.
The same thing would be very neat for composer. So if you want to install the Symfony PHP framework you just enter composer install symfony/symfony --save.
In addition to the "--save" option a "--save-dev" option would be nice. That would add a dev-dependency. For example composer install phpunit/phpunit --save-dev
PS: I hope this feature wasn't requested already, at least I couldn't find an github issue for that.
composer require ... http://getcomposer.org/doc/03-cli.md#require
Thanks @cs278
Most helpful comment
composer require ...http://getcomposer.org/doc/03-cli.md#require