Loose, breathable and easy to clean, they cover most of the requirements for maintaining comfort (to the extent that's possible) while still looking presentable should you be asked to enter the dining room for any reason.
One word of caution, though: most of these collections only offer things you'd want to wear UNDER your clothes; they don't leave much room to wonder whether or not that corset/bustier/bra top is presentable for public.
The primary way to deal with this is through attitude - cheerleaders wear Spankies or bloomers which are completely presentable and go at their routines with all the enthusiasm and spirit they can muster.
When you're on vacation and you're moving from the beach to a restaurant, you want to be able to throw a coverup on your child and go, without having to think too hard about whether she look presentable.
Likewise, men should not wear ill-fitting clothing and should ensure they are properly groomed, so as not to appear as though they could not put forth the effort to be presentable for the occasion.