On a database created on 2005 or 2008, no difference at all. On databases created on those versions, data purity checks are done by default.
On a database created on 2000 (or before) and upgraded, that option forces the data purity checks (see Books Online for details) as those checks are not done by default until a data purity check has run successfully.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability
We walk in the dark places no others will enter
We stand on the bridge and no one may pass