Whether it's by hook or by crook, I think it's important to find out how your manager's bonus is calculated because it will directly affect your working conditions. You can ask in an interview, do searches, etc.
Most manager's bonuses are based on profitability. If you are in a knowledge/service based industry, most gains and losses will be in staffing. I think it's important to know if your manager has a financial incentive to overwork, understaff, or underpay.