Recently whilst visiting a client they were moaning about the lack of true content preview in joomla.
There are plenty of tricks you can employ to preview content in hidden categories etc but its still not the same as previewing the content exactly where it will appear.
The same is also true when adding a new component or plugin to a live site. Will it work properly in the site configuration, what will it look like, will it needed styling to match the site etc and all in an environment where the casual site visitor will not see it.
The web was meant to be read, not squished.
This isn't the way to test a responsive design.