It's a mixed bag. If you leave them closed during the day, people will assume you're not home - but who leaves their drapes open during the night? Even with a light on, how many times when walking down the street at say 3 AM do you see drapes open and lights on?
On the one hand, if you leave them open with lights on, it might deter would be robbers for the simple reason they don't want to be seen. But then again, how many people are out walking in their neighborhood at three in the morning to check for would be robbers?
Even if you did leave them open, it's an easy matter to turn off the lights and close the blinds.
If it were me, I would close the drapes, put timers on the lights and even put a timer on a radio or television to kick on and off. Additionally, share with a trusted neighbor that you are going out of town and ask them to keep an eye on the place. It might even be a good idea to contact local law enforcement and ask them to drive by on occasion.
Long story short - I say close those drapes.