Well, it's a small thing but being able to leave on a moment's notice and not having it considered a breach of contract is helpful.

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.

Whether it's ridiculous or not is a matter of perspective. In Europe the minimum is 1-3 months, though there's often a trial period where the obligated notice is 1 week or less.

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.

This is indeed in Europe.

Again, I don't really mind, but it was surprising.

I sincerely doubt that the contract that you are in is enforceable.

If you just stopped going to work one day, and didn't tell anybody, there is nothing anybody could do about it.

They can sue you if you're in breach of a contract. However, unless it were some special circumstance, I expect they'd make do with just withholding any payments.

In exchange, the employer also has to give as much notice before firing you, right? I would say that's a reasonably fair trade.

In India four to six months notice is extremely common requirement.

The employee can take another job whenever they want to? The alternative is a contract that says I can't fire you absent these specified reasons for X period of time and you can't leave absent these specified reasons no matter how much you hate it.

Given the inherent imbalance of power, another alternative is to remedy that imbalance by giving the favour of flexibility to the worker rather than the employer.