Thecookbook page on extensions recommends avoiding semantic configuration if it's not needed:

When you create a bundle, you have two choices on how to handle configuration:

Normal Service Configuration (easy):
...

Exposing Semantic Configuration (advanced):
...

The second option - which you'll learn about in this article - is much more flexible, but also requires more time to setup. If you're wondering which method you should use,it's probably a good idea to start with method#1, and then change to#2 later if you need to.

On the other hand, thecookbook page on bundle best practices recommends using semantic configuration even in simpler applications:

To provide more flexibility, a bundle can provide configurable settings by using the Symfony2 built-in mechanisms.
For simple configuration settings, rely on the default parameters entry of the Symfony2 configuration. Symfony2 parameters are simple key/value pairs; a value being any valid PHP value. Each parameter name should start with the bundle alias, though this is just a best-practice suggestion. The rest of the parameter name will use a period (.) to separate different parts (e.g. acme_hello.email.from).
The end user can provide values in any configuration file:

# app/config/config.ymlparameters:    acme_hello.email.from: fabien@example.com

Retrieve the configuration parameters in your code from the container:

$container->getParameter('acme_hello.email.from');

Even if this mechanism is simple enough, you are highly encouraged to use the semantic configuration described in the cookbook.