I have done the DBCC DBREINDEX on a 180+ GB database. It did not increase the database (.mdf) file. It DID increase the log (.ldf) file by quite a lot.

The end result was that the .mdf file was SMALLER and the .ldf was LARGER. Why? Well the .mdf has the index data and the reason to run DBREINDEX is to fix fragemented indexes. A fragged index is one that is spread over more pages than it needs to be. So when it's reindexed, the index takes up less space - which equates to a smaller .mdf. However as it drops the indexes prior to rebuilding them, it needs to store the 'original state' in the log file so it can rollback if necessary (it's an all or nothing action).

Once the dbreindex is finished, just truncate the log file (BACKUP LOG dbname WITH TRUNCATE_ONLY) to reclaim the extra space.

-SQLBill