Database connections: to persist or not to persist?

Persistent database connections can be helpful in high volume web applications. OJS 2.x supports persistent database connections in

Does anyone have any practical experience with at what point persistent database connections really offer any benefits?

We have two different architectures, each multi-journal: One multi-install, multi-database; Another single-install, single-database.

For other larger users, do you usually enable or disable persistent database connections?