What happens if I delete all the rows that represents a post revision from the posts table into WordPress database?

You can also do it this way – plugin free.

Open phpmyadmin, browse over to your wp_posts table and:

SELECT * FROM `wp_posts` WHERE post_type="revision";
to see all the posts, their types and revisions and
delete from `wp_posts` WHERE post_type="revision"

Though afraid at first…I did it. And it worked without any impact to the site.