The idea is to add a support for other databases in Drupal installation, specially all the open ones like SQLite3 and PostgreSQL.
This can be helpful to solve some MySQL database problems like have incompatibilities with old versions, or allow to use a more robust DBMS for very large databases.
Put a selector to allow to use other DBMS will just requires to change this configuration for SQLite and for PostgreSQL will also only change the current panel API (like cPanel) to use their PostgreSQL support.