http://symfony.com/doc/current/cookbook/logging/monolog.html#usage should maybe mention the new use_microseconds parameter that was added in 2.11 (https://github.com/symfony/monolog-bundle/releases/tag/2.11.0).

It lets you disable microsecond precision, which speeds up log generation a tiny bit. It's kind of a micro optimization but if you log a lot of debug messages it can matter.

monolog:use_microseconds:falsehandlers:...