The thing that makes a difference as far as viewing and loading images on the internet is the file size. The ppi/dpi only makes a difference for printing. File size is determined by the amount of compression, not the ppi/dpi of your image. It is not neccessary to change the ppi/dpi to 72
because you can have two identical images one sized at 500x600 and 72ppi, and another one sized at 500x600 and 300ppi and if the compression is set the same for both images, they will both be the same file size. However, if the compression on the one that is 72ppi is less, it will have a higher file size than the one that is 300ppi
. And they will only be viewed at whatever res the viewing monitor is at anyway.
Often I see images with a very large file size and the person who posted them has done so thinking that changing the ppi/dpi to 72 will make them load faster. Not neccessarily so folks. The less compression, the higher the file size, more compression means the file size drops. The trick is to find the magic # for acceptable file size for ez loading while at the same time giving you a good image for viewing.
I only learned this myself a few months ago and was quite suprised. Here is two identical images with only the compression factor changed to give you an illustration.