Standby databases are primarily used for high availability,
most of the time they spend being in a state of constant recovery
(process of applying of archive logs from primary database).
End-user access is impossible when standby database is in recovery mode.
If primary database fails, standby database can be activated quickly
and downtime is usually quite low (15-30 minutes). But once activated,
the standby database can not be placed back to recovery mode and
must be created again if needed.

In Oracle8i standby database can be temporarily placed into read only mode
and then back to recovery mode. End-users can run various reporting
applications when the standby database is in read only mode.

But in read only mode archive logs can not be applied to standby database
and it will lag behind the primary database. If the primary database fails,
the standby database can be far behind, its activating will require applying
all accumulated archivelog files, and downtime may increase too much.
For this reason, standby databases are kept in recovery mode most of the time.

If you are interested in reporting database only and don't consider
high availability issues like minimizing downtime etc., you can keep
standby database in read only mode all the time, and place it into
recovery mode only for refresh, to apply accumulated archive logs
from the primary database.