There are a lot to French houses with window shutters, as a general rule are they used and closed at night or are they purely decorative?
I go around the house shutting my shutters in summer (windows open) before the sun is beating down so rooms don't get too hot for comfortable sleep later, & open them again once that bit of the house is in the shade. In winter with the windows shut as well they keep the cold out. When we're away I hope they keep burglars out!
Shutters closed here for security however, check with your own insurers as to how long if you are leaving the property unattended before the closing of the shutters is a requirement for burglary cover to be in force.
We tell all our guests to close the shutters at about 10:30 during the summer to keep the heat out of the bedrooms during the day. Usually they ignore the advice and throw them open and then try to sleep in a very warm room!
I believe that their original purpose is for security. We put in a sliding glass door on our dining room and were told that we had to have a special, heavy duty type glass if we were not planning on having shutters. For us, we close the shutters in the bedrooms at night (mainly to keep the sun out in the early morning) and we leave all the rest of them open unless we are going on a trip in which case we close all of them. I heard that if they are not closed, insurance companies do not necessarily have to comply with paying out if you are robbed.
Just what I've heard...
It also depends on where you are. We close our shutters in winter at night to help keep the house warm (it gets mighty cold here in winter) & tend to shut them to in summer to keep the house cool. We don`t have curtains at any of our windows except the downstairs B&B room which needs them for privacy.so we use them all the time.
Could be viewed both ways, but certainly in summer with direct sun shine on the house I keep mine closed. Also many insurance companies will insist on shutters or metal bars on lower level windows for security (if its a holiday home especially)
I have taken down all the shutters at the front of the house. It looks much better without and as I have never closed any of them (can’t stand being shut in) they were useless.
As to being required by insurance companies, this is correct, in the case of a robbery they may not pay out.
However I had an interesting discussion with my Insurer who agreed that when thieves see shutters closed they often pay attention to see if there is anyone opening them from time to time, if not, it’s a big signal that the owners are away!
Secondly it is so easy to jemmy open shutters (he agreed) that I really don’t understand the requirement for them . His reply, nor do I but that’s the way it is ! 
Hi Ann… we had the Insurance man look over our ruin, shortly after purchase. He talked about shutters…and looked at the various window openings.
One of the smaller ones was , he reckoned, above a certain height from the ground… and therefore needed no shutter. He recommended shutters or grilles, for all the windows which were easily accessible. He even checked the front door and the size of the ancient grille which was behind the glass section… checking that no-one could break the glass and put in their hand to grab the key… (that sort of thing).
It was a fascinating visit…
We shut everything up against the cold/heat… and this sometimes causes consternation amongst neighbours/friends who think we are ill/collapsed etc… it is so nice to know they care …