When enabled, this phpMyAdmin install is set as the system-wide default. A "Manage in phpMyAdmin" button will then be shown on the "Edit Databases" page for domains that do not have their own phpMyAdmin install.

Which phpMyAdmin is used depends on what is installed:

- If the sub-server has its own phpMyAdmin install, that install is used
- Otherwise, if the top-level virtual server has phpMyAdmin installed, that install is used for both the top-level server and any sub-servers that do not have their own
- Otherwise, this system default phpMyAdmin install will be used

This can be useful when you want one shared phpMyAdmin instance (for example, under a dedicated hostname like `pma.example.tld`) while still allowing per-virtual server installs when needed.

Beware, only use a shared "system default" phpMyAdmin under a dedicated hostname if you fully trust the virtual server that hosts it. When other virtual servers do not have their own phpMyAdmin installed, they will use this default instance, which can mean their MySQL login details are passed to it for sign-in. If the hosting virtual server is compromised, misconfigured, or controlled by someone you do not fully trust, those credentials could be exposed.