As notice periods are recognized and written into law (the law says that minimum 30 days or whatever your contract says), they can sue you for lost profit. It's basically that your contract is not up, not finished until your notice period ends, so the same enforcement applies as if you won't show up for work some day. You are still a full-time, fully recognized employee until your notice ends.

But breaking it is not really a thing here: we are used to it, and it's actually recognized as mutually beneficial. If they fire me, I still have 2 months of sure salary and if I resign, they have 2 months to look for a replacement.