I was mainly talking about attached photos. Resizing the pics allows me to download an attachment faster...at least on my computer. Plus those members who post a large attached image causes me to scroll across to read the text or see the whole image. Kind of annoying on my end.
You may already know this but FWIW, an image's file size is length x width x 3 (for each color: red, green & blue.) Change the dimensions and it's smaller so it uploads and downloads quicker. Compressing replaces similar values with a code that saves space: i.e., all the red pixels get coded as 1 rather than 12345, or whatever red's numeric value may be. The compressed file also contains the key to the codes so the colors can be replaced when it is decompressed. The original size is not changed.
As an aside, jpg's use a lossy compression algorithm, meaning they throw data away to save more space. Thus red and near red are considered the same. Saving and resaving jpg's gradually destroys color. That's one reason cheap cameras & phones have poor color, esp. in flesh tones, since they treat all the variations in a person's face as one cor to cram more images in memory.