"I like to travel with a carryon size suitcase, which often means I have trouble packing for the return because of items purchased. These compression bags are the answer - they shrink the volume significantly. I bought the SML set so I could try the different sizes and I'm glad I did. I had thought only the S and M would fit in my bag, but they do shrink quite a bit in dimension once packed and compressed. The M and L will be the most useful."