Minimum connection pool size default behavior


The MongoDB documentation states that the default minPoolSize for the Connection Pool settings is 0:

The minimum number of Connections that MUST exist at any moment
in a single connection pool.
If specified, MUST be an integer >= 0. If maxPoolSize is > 0
then minPoolSize must be <= maxPoolSize
Defaults to 0.

Can someone expand on what it means to have a minPoolSize of 0, i.e. explain what MongoDB does if there are 0 connections?

Are there any performance or other implications when increasing the minimum pool size to greater than 0, and having at least 1 connection in a connection pool at all times?