Question?

I am new in modding REZ file. So far I know how to use Injector and Extractor ( -Sp0ng3b0b- tools), and I know how to change skin of some guns, then rename Mod file to RF130.REZ.
My Question is: My RF130 file is large about 168MB, but I see people post their project and their RF130 is about 4.36MB which is smaller than my file a lot. How they can do it?

Which could get them ban, I guess, Sp0ng3b0b's thinks its Fine as long as the Site they're sharing is in MPGH.net only