There is an advantage to reduce image files, let’s consider that you are sending more than hundred pictures to someone then you can optimize all of them together and compress it using winzip or winrar so the overall file size is reduced.
Talking about PNG files, these are transparent lossless data image files. And incase if you want to reduce PNG image file size then here are some online optimizing tools, though the only disadvantage is the need to upload PNG files one by one but still, it’s free to use and helps in PNG size compression.
The first one, the popular service owned by Yahoo! is called Smush.it which allows compression up to 5 images at a time. You can also make use of the addon (Yslow) that is available for Firefox browser users. Smush.it works pretty well and reduces image size of PNG, GIF, JPG and other image formats as well.
Another notable online tool is Puny PNG, which is a side project that acts as an online optimizer helping you to compress the image size to a greater extent.
Not only can you optimize PNG image size but also upload JPG file and curb down the size, though the quality of the image might differ from the original, slightly!