I have had trouble with cropping post thumbnails since 2011. I mean sure I can open up Photoshop, but sometimes you got an image and you just want to crop it just a bit to the right. This plugin just smooths that whole process.
I gave 5 out of 5 stars purely because the functionality of this plugin is excellent.
It's embarrassing that WP doesn't even have this functionality (it only can edit thumbnails for the admin to see at media).