Persistant connections are great for sites that are not under heavy load. (many users online at once) The persistant connection will be faster as it's not dropped and can be continued to be used by the visitor. I believe the max is 200 ? for persistant connections to MySQL but I could be wrong. If you have 250 users online some will get the error "to many connections" from the database. If you don't use persistant connections then as soon as a user gets their information the connection is dropped and is then available to another user. This is what helps the greatest on busy sites.
