The “extra packages” in MikroTik RouterOS are used in situations where you need additional or specific functionalities that are not included in the basic installation package.

These extra packages offer a variety of tools and features that may be essential for certain deployments or to optimize the network to very particular requirements. Here are some scenarios where you might need to use them:

1. Advanced Network Services: For deployments that require advanced services such as MPLS, BGP, or advanced routing that are not included in the basic packages.
2. Enhanced Security: If you need additional security features, such as IPSec, advanced VPN tunnels, or advanced firewall.
3. Network Management and Analysis: To implement advanced network monitoring and management tools, such as The Dude, advanced graphics tools, and SNMP.
4. Specific Hardware Support: Some extra packages may offer support for specific hardware that is not supported by default, such as certain types of wireless cards or optical modules.
5. Application Specific Functions: If your network needs to support specific applications or services such as email servers, web servers, or VoIP gateways that require additional packages.
6. Updates and Testing of New Features: In some cases, you may want to test the latest features or updates that have not yet been included in the main package but are available as extra packages.

It is important to mention that before installing any extra package, you should make sure that it is compatible with your version of RouterOS and that you understand the security and performance implications it could have on your network.

Installing additional packages should be done carefully, ensuring that you really need the additional functionality they offer and that you are prepared to manage any additional complexity they may introduce to your network.