In Spain you may resign before, but they can subtract for each missing working day to the notice period end the money they own you (it is a penalty, not just discounting from salary the days you are not working). In some cases leaving workers use their remaining PTO days to exchange to leave before the period of notice as they have the same value. So in Spain a greater period of notice can result in bigger penalties when leaving a company, while companies can fire you on the spot (paying the required severance).