Summarize this article in one sentence.
Compression fabrics are tightly woven to help increase the circulation in your legs. If you're engaging in an intense workout such as running or kickboxing, they can help reduce your soreness following your workout.  Compression leggings tend to be more expensive, so unless you're engaging in high-intensity activities they may not be necessary. However, they have an added benefit of making your legs look taut, your muscles more defined. So if money is no object, you may prefer them for this reason alone. You don't necessarily need a compression-style legging if you're going to be wearing them mainly for yoga, and you may find compression leggings a hindrance. You do, however, need to choose a fitted style that won't interfere with your poses.  Remember that in yoga, you may very well be bending over with your butt in the air, so before buying leggings, make sure you can bend over completely without exposing more than you want, and make sure the back of the leggings aren't sheer when stretched over your backside. Wearing fitted leggings also will allow your yoga instructor to check your form, which they may be unable to do if you're wearing looser clothing that conceals the position of your body. Additionally, many yoga poses require you to balance one foot on the other leg, or grip parts of your leg. This can be difficult if you're wearing loose clothing. While your yoga leggings should be fitted, they shouldn't be tight or constricting. Pick breathable fabric and an elastic waist that allows you to breathe deeply and doesn't pinch. If you're going to be wearing your workout leggings when lifting weights, hiking, climbing, or other activities where your freedom of movement is paramount, a relaxed fit will be an asset.  Looser fitting leggings will allow you to move comfortably without worrying about a possible "wardrobe malfunction." For activities that might involve abrupt movements, you don't want your leggings to get in the way or restrict your range. Looser fits also may be more flattering for these kinds of activities. Keep in mind "relaxed" or "loose" doesn't necessarily mean "baggy." Pants that are too big and don't fit properly can trip you up and cause significant problems.
Look for compression styles for intense activities. Buy fitted leggings for yoga. Get a looser fit if you need freedom of movement.