It's insignificant. Find better ways to save energy.
Your typical laptop consumes less electricity than one average light bulb.
This is a brilliant case of being penny-wise, pound foolish.
Laptop = 15-60 watts.
Light bulb = 60-150 watts
Fridge = 200-700 watts
Dishwasher = 3500 watts
Clothes dryer = 4500 watts
Are you planning to turn off your fridge every time it's cold enough and turn it back on just in time to avoid spoiling your food?
Energy saving should be an analytical activity. First, identify WHERE most of your energy footprint comes from, THEN figure out ways to reduce it. Don't fall for feel good, knee jerk measures.
Edit: Following your comment about electricity prices in Germany, here are some REAL numbers for you to think with:
Assuming 4 hours per day, 365 days per year, with a laptop consuming 50 Watts, you are using 76 kWh per year.
According to https://secure.wikimedia.org/wikipedia/en/wiki/Electricity_pricing:
1kWh = $0.306 (Germany - 2009).
76 x 0.306 = $22 per year.
If, through great efforts on your part, you saved 30% of your laptop energy consumption, you would reduce your yearly electricity bill by $7.
Do you really feel it is worth it?