I've got a letter I send out about once a month, just changing dates in the contents for each edition. It has a linked .jpg file as background.
In StarOffice 7 the .sxw file size is 8 Kb.
In StarOffice 8 the size has leapt to 44 Kb, whether I save it in .sxw or .odt format.
Why?
I find that file sizes increase both with text documents and with spreadsheets, sometimes by a great deal. One of the reasons I switched from 5.2 to 7 was the much smaller file sizes, since I keep my weekly back-ups on floppies (and am a stingy sort of fellow generally). But I had to run 7 and 5.2 together, since 7 does not handle Sanskrit/Hindi founts (the SO "help" team just asked a whole lot of questions and then disappeared). So now I have (on Windows) 5.2, 7 and 8. I have still not checked if 8 handles these founts. If it does, I can remove 5.2. For the rest, 8 does not seem to offer any advantage over 7 -- not counting the data base, which I have still to look into. File size, in my view, goes against it.