COMPLETELY ruins your website

I’ve only tried this on 2 websites but each time it distorted the images either making them to wide for browser or on another site. Seeming moved them. The front page image was pushed up chopping off the head and leaving a big space before the rest of the page.
I get the feeling that this needs to be installed from the very beginning on your site design and does not work when installed on an already up and running multi-page website?