Plain MySQL connections are exceptionally quick to set up - much more so than many other DB options. For this reason, many people have written code that does not use connection pooling (coughPHPcough), and instead create new connections at whim. This is why it's worth pointing the differences out.
As a point of contrast about the side effects of this connection speed: The standard Python MySQL library does not even offer connection pooling - you would have to write your own or use a ORM that provides pooling. On the other hand, the most oft used PostgreSQL Python library offers connection pooling for free.
Not saying one method is better than the other, but it's quite possible to write a performant solution using MySQL that doesn't pool connections.