One of the most important things that I've learned is that you can only be up to 100% efficient - you can't get 25 hours of work done in a day. How do you know when you're at the point of diminishing returns?
We all want to believe we can add one more thing to our plate without it being a problem. But there's only so much time in a day, and that tiny one-more-thing can be what tips the balance. Have you seen the last scene in the Meaning of Life by Monty Python? A huge man is eating a gigantic meal. At the end, he's offered a tiny, wafer-thin mint. He eats it and explodes.
The two indicators I look at are my stress level and my slack space. If I have so much on my plate that I'm constantly thinking about the next thing and always rushing to get stuff done, that's an indicator that my time is pretty much full. I'm at that point a lot at the moment, actually.
You can also consider whether you have enough slack time in your schedule. You need slack to handle unexpected work and personal things that crop up. If a single slipped schedule or car breakdown throws your whole life into chaos, you probably have too much on your plate and need to drop something.
Becoming more productive at what you currently do can, of course, free up some time. But even that isn't a panacea. It takes time and effort to find alternate ways of doing your work, and then more time and effort to implement those. At some point, it takes more time and effort to improve your performance than the time and effort you actually save from improving.
When you've reached that point, you're doing as well as you can. If you're still overloaded, it's time to remove things from your plate so you once again have room to breathe, relax, and cope.
Courtsey : Stever Robbins