We must and should optimize every image, before uploading it to website going to live. Optimization of images is nothing but we have to limit or fix the resolution of the image. standard web resolution of images is 72 pixels, we have to follow this rule while designing website. If we will upload large size high resolution images directly, they will take longer time to load. Especially in home page banner and other content based pages images should be optimize in photoshop, that is 'save for web devices'. Short cut key is: CRTL+ALT+Shift+S.