When default product variant stock reach 0, this module automaticaly changes variant with highest stock to default.
It prevent to show label "out of stock" on Homepage, when default variant will be selled of.
You don't need to use phpmyadmin to make some changes to your Prestashop's SQL base. Using this module you can connect to your base straight from your shop, no need to log in by phpmyadmin. Useful thing for Prestashop administrators.