I am in a financial services firm where we work with Microsoft Excel
all the time. The files are very large (50MB on an average). The files
contain lots of numbers, named ranges, VBA macros, heavy formatting
with colors and tonnes of addins.
I am trying to find out ways of reducing file sizes.  My question is specific:

I want to know what causes the file size to increase and in what proportion. 
For example, most of our sheets have data scattered around. So if i
use the function ActiveSheet.UsedRange.Address, it will return
something like $A$2:$HJ$6095  (huge dimension), although most of the
cells may be empty.
I could realign the data so as to reduce the UsedRange, but then i am
not sure how much difference will it make to the file size.
If i know that coloring causes file size to increase drastically, i
can try to optimize this parameter.
Basically, i need to konw what factors affect the size of the file,
and in what proportion

Hi oxymoronpointer, here are two useful links -

Honey Can I Shrink the Spreadsheet ?
http://www.beyondtechnology.com/tips019.shtml

VBA Code Cleaner:
http://www.appspro.com/Utilities/CodeCleaner.htm

Regards,
hummer

Excel Diet:
http://www.vbaexpress.com/kb/getarticle.php?kb_id=83