You could consider performing a takeover when the primary database will be unavailable for an extended time. (See also "Negotiated Takeovers", earlier in this chapter.) In some instances, it might be less disruptive to wait for the original primary system to become available again, rather than to perform a takeover.
You should base the decision to perform a takeover operation on the following considerations.
If the primary host or the network has failed, the time required to restore them or to revert to backup hardware at the primary site
If the primary database has been damaged, the time required to restore the database from backup using standard restore and recovery techniques
If the journals on the secondary are behind, the time required to synchronize the database
If the journals cannot be synchronized due to a primary host or network failure, the impact of losing transactions or having to reprocess transactions