This article explains resource allocation when performing WIR or VMware Instant Recovery.
WIR will use backup system processor (CPU), memory (RAM) and storage (pulled from the Failover Virtualization setting). VIR will create an NFS datastore that pulls storage from the Failover Virtualization setting allocated.
These resources need to be considered in use all the time. They are not, but should be considered so in order to not over utilize the backup system. The WIR interface will show you when you have over allocated your backup system's resources.
Keep in mind that your backup system will still be performing backups, incremental forever tasks, deduplication and vaulting tasks, and will be available for restores. The more resources you allocate to WIR and VIR the less there is available for the other feature sets.