The old problem of absenteeism has a curious mirror-effect we call Presenteeism – the psychological need to over-attend. Redundancy fears focuses the mind on attendance and often translates into presenteeism.
One of my clients was living in perpetual fear of redundancy, and believed that it would safeguard his job if he was seen to work all hours. When he caught a bad cold, he still insisted on coming to the office, and it turned to pneumonia, which eventually forced him to go off sick for a fortnight. You can see how unwise it is to attend when ill. Unwell employees are not going to perform efficiently anyway. At worst, it could lead to some catastrophic error or spread infectious diseases around the office.
You should note that long hours do not always translate into more effective output, and that they may stem from inefficient time management anyway. Managers should also check that they are not setting an example of working over-long hours, which their employees are trying to emulate.