Here is a short but useful piece of advice when it comes to saving your JPEG files:
Save them at 90% quality.
It saves space on your hard drive like you can’t believe.
It saves you time when uploading to your photo site(s).
They look the same as if you saved them at 100%.
You take advantage of the JPEG compression algorithm, using it for what it was meant, where at 100% you do not.
Almost none. Some stock photo sites will want you to upload at 100% quality (no compression), just because they are who they are and can tell you what to do. I would defy them to show a difference in a photo at 90% quality (10% compression) from one at 100% quality (no compression).
So, save yourself some time and money by compressing to 90% quality when you save those JPEGs!