Well, if you're mainly concerned about any winter freeze that may take place while you're gone, I think turning off the water to outside faucets could work to your advantage..
Remember to open the valves of the water spickets that run outdoors though or any existing water in the pipes would freeze regardless of whether you shut the main valve or not.
If you plan to completely shut down the heat at home, you're actually exposing yourself to multiple freezing problems, though. I'd say make sure you have sufficient heat circulating at above freezing, Paul.
Sure no reason not to, but if your doing it for prevention of freezing then Ricardo has the best idea keep the house heated. However as a precaution to a broken pipe while your away, good idea. Just be sure to put your hot water heater in vacation mode. This leaves the heater on, but only the pilot light remains. If for any chance a leak did develop and the heater drained out you would not want to have it turn on while away and burn up.
If you do decide to turn off water for freeze protection, Flush toilets then put anti-freeze in both bowl and tank and then pour a cup in each sink and tub/shower area. This will prevent the traps and toilets from breaking.
I'm from Sydney, Australia so there is no worry about freezing weather or frozen water pipes. I've never turned off the water, but if we were to go away for a week or more, we turn off the gas flame. As our gas hot water is an 'instant recovery' system. So it keeps on reheating when it doesn't need to.
If you cut off main water supply it is possible to burn up hot water heater so you have to turn off water heater also