It is highly suggested to enable the “Magmi Magento Reindexer” plugin.  This plugin will perform a reindexing of any of the Magento Index tables after the import has completed.  Reindexing will speed up the site as well as fix some issues related to products not showing up correctly.  If you have added / modified products and they are not showing correctly in the store, one of the first steps is to reindex the site.