A useful time saver

As others have said, if you spend the time to optimise your images before you upload, then this app is not needed. The upside is that you don’t need to worry about that side of things so a) your workflow increases b) as long as you set the compression level up on the app your quality isn’t adversely impacted. To be honest though, even if the quality does drop a little, I would rather trade that with the increase in site speed.