In addition, you may calculate how many generations you need from what data for 
capacity planning:

Database files are usually saved full- if one has 200 GB database files and 10 
generations,
this means 2 TB!

On the other hand, the Client os and application like Word processors and 
Spreadsheet progs are
 saved once and never again (up to the next update) and needs only place for 
almost one copy.
But care for software distribution - your backups may crash if there is a 
enerprise-wide update
of local client software which has to be backed up on all systems!

Documents like texts, spreadsheets etc. usually don't have much change 
activity, most
of them will only have few generations (Companies may differ in this behavior).

One should think if the backup of client os and application is necessary - 
having 600 pc's
with NT and MS Office means some 200 MB identical files for each node - 120 GB 
tapes needed,
and all scanned for changes in each backup process.

Regards
Roger