The command-line arguments to append to Godot's own command line when running the project. This doesn't affect the editor itself.
It is possible to make another executable run Godot by using the [code]%command%[/code] placeholder. The placeholder will be replaced with Godot's own command line. Program-specific arguments should be placed [i]before[/i] the placeholder, whereas Godot-specific arguments should be placed [i]after[/i] the placeholder.