In the last weeks I have worked at 100% - I have slept not more than 3 to 5 hours but needed to fully concentrate during the day and nights. In between I was on full speed handling children or parts or other work in the household or somehow related. - A reason why I did not post here for a while.
This works for some weeks but then it comes to an end. The last days it was already very difficult to concentrate and be productive. Fortunately I had a deadline to be kept so I did know exactly how long my energy must last.
So my important advice for employees: If you need to work extra hours, make sure that it is for a limited time only. Know the goal, mission and see the end. Example: If a colleague has left the company and your boss is not going to fill the gap expecting you to do the work from now on working more then this is not such a situation (assuming that your normal work is not reduced at the same time)! - Effect: You will loose power and at the final end although working more hours your boss will complain about less productivity.
Important advice for companies: Know, that your employees have not everlasting batteries. Massive extra hours should be reserved for emergency! This should not be a normal situation! The power of your employees will get less and hence productivity, creativity and they/you will have no more flexibility to adapt in emergency cases. Even if you try to hide it, somehow your customer will notice due to reduced quality, slower response times etc.
Related posts: Parkinson's law and quality, Stop the service, Reduce the stress factors.