The items in the pictures are from Cosmolle.com [from top left]
This is a use that I discovered myself fairly recently. If you have a mesh or opaque dress (and you don't want people to see through to your regular underwear) shapewear can be a great alternative. The skin colour design of some pieces gives off the effect of wearing a bodysuit, like dancers wear under their outfits.
Helps Clothing Fit better
Clothing tends to be made for average body portions, but people rarely fit into that category. If something fits my waist, it won't fit my hips and thighs. The right shape wear can reduce the dress size of certain areas to help make your clothing fit. The more traditional pieces can be particularly good, like the tummy control shaper panty. I think shapewear doesn't have to be about 'trying to look better' it can be about practical things too.
Smooths out an outfit
This was something that Kirsten Wiig pointed out in an interview and I do think it makes sense. If you're wearing a body con or tight fitting dress shapewear can smooth everything out so the dress flows correctly. How something flows is one of the most important things when it comes to clothing, and people often overlook good tailoring these days. Sometimes, those kind of dresses can pucker up in places or not fit correctly in others so the shape wear helps with this.
Good for the gym/extra support
If you have a shapewear top or a pair of high waist shaping shorts they can help to support certain areas. If you're in the gym or doing exercise it can become painful if your breasts have a larger cup size. The shapewear offers the extra support to give you some comfort. It can also help with this in everyday life too, if you live an active lifestyle... or just in general if you like the feel of tight fitting clothing.
Helps Blood Flow
I didn't know this, until I read this article, but apparently shapewear can help with blood flow. Apparently, there's been a number of studies on it and many brands design them specifically to help boost thermal activity. This extra boost helps to increase weight loss. If you're looking to diet and help reduce toxins in the body, then this one is for you.
I want to add in a little disclaimer here and say that weight loss should be an individuals choice and handled in a sensible, healthy way. It's so easy to drop underweight or become ill if you approach it for the wrong reasons, in the wrong way. All shapes and sizes are beautiful and should be celebrated.