Size reduced and delete

Hi, does this plugin also reduces images size? I wanted to convert for a fastest site but I am also interested in reducing size of the images in my hosting, so I’m not sure if I can accomplish both as I read they also keep original image.

Also, if I want to delete an uploaded converted image that I no longer want to use, is deleting from WP media menu enough or I need an extra step? As I read converted images are stored in another folder.

Thanks