I think Save for Web also has a slice tool built-in that you can use to partition an image. I don't remember if PS has that, but Illustrator does, and I'm pretty sure they're using the same code in both places.
And yes, Save for Web generally produces smaller files for some reason. It also gives you an interactive preview of the exported image and a readout of exactly how large the saved file will be. And a 4-up view that you can use to compare different compression ratios and file types. I love it for optimizing my PNG exports.
you are right" Saving for Web is really nice. I got better resolution with it.
Thank you very much!