I used to struggle with image optimization, CSS, and unnecessary JavaScript code
The plugin that I used before – Autoptimize, was ineffective
It added too much unnecessary code
But Jetpack Boost accelerated my site’s speed significantly after enabling settings concerning CSS, JavaScript, images, and CDN
Images load instantly, as well as the site content itself
Lazy loading feature also helps greatly, as it only loads images when necessary
It works extremely well in pair with WP Super Cache, I recommend this combination to everyone who uses WordPress.