WP Smush is an award-winning plugin that has well over 800.000 downloads on the official WordPress site.
What Smush does is very simple yet important for any website with images. It lets you compress, resize and optimize any sort of image within seconds. And the best thing is that it is completely free. You can upgrade to pro version but only if you truly want to.
So if your website is loading slowly or just, in general, you should definitely install Smush.
Does anybody currently use it for their websites? How are you liking the plugin?