Absolutely! You only have a few seconds to make a good impression, generally, about 5. Many don’t pay attention to the file size of the images they upload to their website or blogs. It really doesn’t matter because it resizes to fit the area I need it to complete, right?
Right, but what you don’t see is the HUGE photo that is being loaded while your visitors wait for it to be resized so it will fit on your page.
Why should this matter to you? If your site or blog doesn’t load quickly, your viewers may move on rather than skip it or wait. This can drastically increase your load time.
Here’s a good article that goes into more detail: http://www.1dogwoof.com/10-tips-best-image-size-blog/