We designers care a great deal about making small image file sizes, so the art and photos we share online and in email will upload and download quickly. There are countless ways to make highly-compressed (optimized) images that will do the trick. Here is the one I live by.
Photoshop is powerful, and it’s bloated. I use it because it’s the best, but it’s not the best for some actions. ImageOptim streamlines my image optimization, which is mission critical, considering the large number of images I edit daily.
Wherever the image came from, I see to it that I compress it with ImageOptim before it’s published or shared (unless of course the imagery is made for print use).
I usually save multiple images at a time, that I then organize in the Finder somewhere (like a project folder on an ext. hard drive, or Dropbox). Then, when it’s convenient, I batch compress them with ImageOptim all at once.