Why do I need to automatize my infrastructure ? Why do I need to automatize my deployment ? How can I do that ?

Today, It's really a need to automatize everything. It avoids human errors. It let focus you on business value. Not the ops details. It makes you confident in your process, production server...

At SensioLabs we use Chef a lot and as a developer (which do a lot of ops too ;) ), I want to share my experience with you.