The feature will make it possible for companies or servers that don't use SAN/NAS with deduplication to save disk space, alot if disk space.
How much disk space you can save will depend on what kind of files you have on the disk. You have a utility you can use to calculate the savings, the tool are now only available when you have installed Windows Server 8 (sort of), but I am quite sure that it will be a downloadable and graphical tool in good time for the RTM release of Windows Server 8. The tool that are in the beta version of Windows Server 8 are a command line tool.
Yes I am running it on something else than Windows Server 8, it's actually my Windows 7 computer. My next blog post will tell you how to run it on other Windows than Server 8
Be aware that all deduplication have the cost of hardware resource usage, so be sure to monitor your server to make sure that you don't replace disk shortage with other system resource shortages. You might also use a dedicated server as storage server, remember that Microsoft now give away the ISCSI Initiator target for free.
You can of course use Powershell with it, so it's easy to automate the process
|Disable-DedupVolume||Disables further data deduplication activity on one or more volumes.|
|Enable-DedupVolume||Enables data deduplication on the specified volumes, using default settings.|
|Get-DedupJob||Returns status and information for currently running or queued deduplication jobs.|
|Get-DedupMetadata||Returns a Deduplication Metadata object for every volume that has data deduplication metadata.|
|Get-DedupSchedule||Returns the Deduplication Job Schedule objects defined on the system.|
|Get-DedupStatus||Returns a Deduplication Status object for every volume that has data deduplication metadata.|
|Get-DedupVolume||Returns a Deduplication Volume object for each volume that has data deduplication metadata.|
|New-DedupSchedule||Creates a new data deduplication schedule and returns a Deduplication Schedule object.|
|Remove-DedupSchedule||Deletes the specified Deduplication Schedule object.|
|Set-DedupSchedule||Sets data deduplication schedule settings.|
|Set-DedupVolume||Sets data deduplication volume settings.|
|Start-DedupJob||Queues a new data deduplication job of the specified type for the specified volumes.|
|Stop-DedupJob||Cancels one or more specified data deduplication jobs.|
|Update-DedupStatus||Scans one or more specified volumes to compute fresh data deduplication savings information and returns a Deduplication Status object.|
Table based on info from Technet
To learn more about how Windows Server 8 implementation of deduplication works you can go to this Techrepublic article