I always have snow chains in the back of the car during winter. For our 2WD it's essential - there's been hills I couldn't get up with just winter tyres. But I have them for our 4WD as well, just in case.
Tips: practice putting them on at home. That way you'll a) know the they fit* and b) you won't be doing it for the first time during a blizzard at -20 wind chill. Also get the simplest. I've had more trouble with so-called easy fits than the standard.
* Twice I've gone on ski holidays with people who've got chains but when they needed to use them, they were the wrong size!
We usually change ours mid to end of October. This year, however, we drove to Barcelona end of September and will return first week of December. Rather than risk France in December on summer tires , we just switched ours out in September before we left CH. We are not driving the car till we leave, so hopefully the wear on the tires will not be excessive.
A few times now, due to the Gotthard tunnel being closed for maintenance and the pass closed for winter, it was necessary to take the San Bernardino tunnel. Due to heavy snow on the Swiss German side, the police were stopping cars and if they had no chains or winter tyres were being turned back. We had a Range Rover 4 x 4 with all year tyres so could carry on - in fact we were one of the very few cars allowed to make the climb up.
Well that's more like it. Just drove over the Ballaigues/Vallorbe border and the temp was 5C. No-one was at French border or checking though.
'Franche-Comté : Quelques flocons de neige prévus dès 1.100m d’altitude ce vendredi' - Franche-Comté some snow flakes expected at 1.100m this Friday.