Steven547,
I defer to what Skip was talking about. I believe with any Shared Workbook (not just a Shared Drive location), you will have a bigger file, especially if there have been many changes. With a shared workbook, there is a history that is stored, so that one person (or group of persons) can approve/deny changes.
When you save a non-shared copy (local or network drive doesn't matter), then you would be dismissing all the history that is involved in that whole approval process (I think) which could easily explain losing some parts of the original file - thus greatly reducing the file size.
I could be wrong, as I don't do a lot with Shared Workbooks, myself, but that seems to me to be the way it is supposed to work.
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"If to err is human, then I must be some kind of human!" -Me