You need these for 2 reasons - - (1) for packing as much as you can into a space and (2) staying organized. I can get about 10 dresses in one large packing cube which is major. I pack the smaller cubes vertically in my 40L Tortuga travel backpack and it allows for even more space. I sometimes even pack outfits inside gallon zip locks and then place them in each cube and only pull out what I need each day of travel. SUPER organized, but always maximizes my wardrobe and keeps everything smelling fresh.