DB_VERIFY performs a physical structure integrity check against off-line database files

The utility runs perfectly well against on-line files as well, however, the manual is clear that it is an off-line utility. My assumption is that it may incorrectly report blocks as bad while I/O is taken place (fractured blocks).
DBA's should use this utility frequently to identify datafiles that are corrupted. Some times the database will perform normally until you address a particular block in the datafile, which may then result in ORA-600 errors.
DB_VERIFY is useful in these situations:
When block corruption is expected; Forecast any future problems w.r.t. database file/ block corruption; When you restore files from a tape. It will help knowing if the first file pulled from tape is corrupt, instead of spending hours to extract all of them. To access help on DB_VERIFY type:
dbv help=y

Example:
$ dbv file=/u01/oradata/o10gr2/example01.dbf
DBVERIFY: Release 10.2.0.1.0 - Production on Sat Jul 7 11:45:52 2007Copyright (c) 1982, 2005, Oracle. All rights reserved.
DBVERIFY - Verification starting : FILE = /u01/oradata/o10gr2/example01.dbfDBVERIFY - Verification complete
Total Pages Examined : 12800Total Pages Processed (Data) : 4409
Total Pages Failing (Data) : 0
Total Pages Processed (Index): 1264
Total Pages Failing (Index): 0
Total Pages Processed (Other): 1539
Total Pages Processed (Seg) : 0
Total Pages Failing (Seg) : 0
Total Pages Empty : 5588
Total Pages Marked Corrupt : 0
Total Pages Influx : 0
Highest block SCN : 470536 (0.470536)