Notice periods are, as far as I know and in my experience, the _minimum_ number of weeks or months to give notice. Nothing is stopping you from giving notice earlier.
It seems like you could really harm a company by forcing them to pay you to nothing if because they don't want to start someone on a project they will definitely leave half way through.
If you continue fulfilling your responsibilities as an employee, I don't see why. If a longer planning horizon is needed, a longer notice period is the answer.
