I had no idea how much space I was wasting on uncompressed PNGs. Then I tried PNGGauntlet, a free program which losslessly shrinks PNGs. I ran it through a screen shot I took and cropped in Paint, and the file shrunk from 85K to 60K.
That doesn’t sound like a huge improvement, but it’s a free 30% drop in size. On a website with a lot of images, 30% less bandwidth can certainly add up to real savings. Even if it doesn’t, making your page load faster leads to a better experience for users, especially on mobile phones.
My plan is to start running images through this and reaping the compression benefits.