The problem with that is that plain script tags can be started to load once the first TCP package of the HTML source code has been received. Your javascript tag

The problem with that is that plain script tags can be started to load once the first TCP package of the HTML source code has been received. Your javascript tag would only be executed after all that has been loaded and the JS parser has been initialized. That can be up to 300ms to 500ms on slow and mobile devices.