Like WP Smush a lot

I have a lot of photos on my blog, so I really needed this plug-in. It works well and has reduced my photos by about 10%. My only issue is that when I add a new photo to my media library while I’m working on a new post and I hit the Smush button, it doesn’t smash. I have to go back later and resmush it. Clearly I must be doing something wrong, but I can’t figure out what.