What's the benefit to the employee?
I was a bit surprised to find that instead of being a matter of courtesy, I'm contractually obligated to give 6 weeks' notice before leaving. I don't mind, really, but it's still kind of ridiculous.
In practice though the employee/employer are free to upon termination sign an agreement reducing the dismissal period to whatever they feel is appropriate. Few employers wants to keep an employee that's decided to quit longer than strictly necessary.
Again, I don't really mind, but it was surprising.
If you just stopped going to work one day, and didn't tell anybody, there is nothing anybody could do about it.