The first is for fashion and keeps you warm if in a Northern climate. Compression Leona are for medical use. .. mainly varicose veins I believe. I don't think exercise other than walking is advisable if wearing compression socks/leggings.

Regular leggings are made of mixed materials, mixed qualities, and vary dramatically by brand and design, as well as health effects. there is no way to determine the effects of a particular pair of clothing-leggings.
compression leggings are tested and measured, graded for their performance and suitability to the diverse sizes and requirements of the medical usage.

This is one of those things we dealt with. Compression helps with moving fluid so as to not it build up in one area. You don't want too much squeeze or you lose all circulation. It's really something you have to watch for tolerance of the limb. My son uses them on his feet if they are swollen for only a few hours. Diabetic socks are good for minimal compression, better circulation and no tightness at the top of the sock. Being from Vegas I've known waitresses and airlines stewardesses that have worn compression stockings from lots of standing. My son is wheelchair bound so we used them just for the foot area. Compression is all about the squeeze. Leggings help hold stuff in but unless it's like a scuba gear material you aren't really supporting anything because clothing fabrics don't have the right pushes and pulls. Kinda like comparing spanx to spandex shorts.

basically, the answer is that one is a medical device and the other is a fashion item. the medical one wouldn't serve well for wardrobe, and vice versa. you CAN get some benefit from a careful selection of the fashion item, particularly if you do not need it for a medical purpose aside from sensory input. for sensory input if its in line with the person's personal tastes you can naturally include it in your clothing habits.

Compression stockings are used for patients in hospital who have had surgery. They are used to prevent DVT'S -deep vein thrombosis; but doctors also give them to patients who are ambulatory. I only know them as for medical use. Leggings have no medical use; but they keep us warm under thin slacks in the winter. A lot of people use them as regular pants. If I want thin pants I use the slim jeans.