Normally JPEGs will load from top to bottom that thing is called baseline images. Progressive JPEGs are loaded differently, in progressive they show the entire image right away, but it loads very pixelated version of this, which will, as the time goes by and data gets loaded - get more clear. See examples below.

Baseline JPEG Example

Progressive JPEG Example

Benefits of using progressive JPEG's over Baselines

Progressive JPEG's can be much optimized much better, which results smaller file size.

You can see the image right away, and since we have pretty fast browsers nowadays the data will come in faster and picture will clear pretty quick as well.

Which one would you prefer to use on your webpage?
I feel like the Baseline JPEG version is kind of outdated and was only used a couple of years ago with the old and slow browsers..
Thanks for reading!