What would Repair and Optimize Wordpress Database do?

Recently I am getting an error establishing a database connection in a clients Wordpress site. I googled for a solution and an article suggested to enable Wordpress Repairs by adding this to the wp-config.php file:

define('WP_ALLOW_REPAIR', true);

After that, visit the link:

http://ift.tt/1ab1nSy

And allowing repair as follow:

So my question is. What does optimization mean? What are those scenarios or situations that Wordpress fix? Can I do this procedure in existing and non problematic Wordpress websites to enhance performance?

via Chebli Mohamed