well you have to remember that data on a computer is binary, i.e., made up of ones and zeros and if you look at the 1s and 0s you see that that the 0s take up more space so they're will definitely cause an increase in weight.
I'd recommend that they (people who are concerned about the weight of their computers) to search the net and find a utility that will strip the data of all 0s and push the 1s together. Besides what's a 0 nothing so why occupy space with nothing