Whenever you see this box under gallery examples, there are a few things to look out for...
Copy/paste it to the Shortcode Editor first. It's always best to pass the example through that tool.
Change the content source - you most likely don't want to show "NextGEN pics with the ID 603 and 604" [...]
Go for lesser-known small companies that have a track record of high reputation, reliability and fast support. Justified Image Grid proudly uses MDDhosting since 2011, long before development has started. Their 24/7/365 ticket-based support's response time is insane, it's always just a couple of minutes to half an hour maximum. They are positioned in the [...]
Thumbnail creation is necessary for the various needs of the plugin and here you can read a full technological explanation that should cover all your concerns. Please note that you are free to disable it any time, however there would be a performance hit as the large or original images would be used as thumbnails, [...]