To explain the title; heres what I noticed today.
I was opening two old projects, f8 format … editing and resaving as cs3.
Nothing interesting happened there, the filesizes of the 2 files changed a bit, but not considerably.
However, when I saved them as f8 from cs this happened
File1 decreased from 8.5MB to 2.5MB
File2 decreased from 13MB to 7MB
Eeeeep? What just happened? : )