These are perfect if you travel from one hotel to another.  Place your evening clothes in one, your casual clothes in the other, workout clothes in the other and pj's/bras/underwear in the other.  Rolling your clothes will NOT wrinkle them, plus you will be very organized without searching and disrupting the other clothes.  No more searching in your luggage for your top or your slacks that may be at the bottom of your luggage.  Plus you get a large laundry bag for your dirty clothes.  Highly recommend buying them.
P.S.  They do not take up space, I think I could have used a smaller piece of luggage.