Is that it??!

I've just installed IH2 and everything seems to be working wonderfully! In fact, it went so well and so easily that I'm assuming I missed something.
Does IH2 automatically resize my existing images? I assumed I would have to do the grunt work of resizing. (NOT that I'm complaining! ) I can see the medium images are in place on my site but am not sure if everything has actually been optimized or not.

Thanks for whatever help you can provide.

Tim