[Plugin: WP Smush.it] What happens to the original image files?

I’ve got a wordpress site with thousands of images. I’d like to run a bulk smushit on them but I’m worried if there are errors, what might happen to the originals? Does the plugin keep a copy of the original?

That said, is there much cause for worry? Anyone run into issues where the plugin devastated their image/media library?

Thanks for any input!

https://www.ads-software.com/extend/plugins/wp-smushit/