To be honest I doubt ever packing more items could make things lighter, surely the weight of each item is the same it's just that they're packed smaller enablling more space in the case.
Unless of course they're packed with helium!

Hmmm
if it did I am sure some diet company would have used the technology by now!
I think they are just to save space but also helps save on creases too.

i have used these bags in a factory for wool,they reduce the zize by removing all the air but the weiht is still the same
garry

We bought some in Walmart when we were in Florida and we have since bought more here in the UK.You put your clothes in and then suck out the air (there is a one way valve).You end up with a flat, heavy package of clothes.It reduces the amount of space taken up in your suitcase but you will need to re-iron the items as they do get creased.