Insurance is great, no doubt, and certainly the first thing to do. But after having an '84 coupe stolen and having to court an insurance company for a couple of months and all the other associated hassles, it sure makes sense to install a simple hidden kill-switch type theft deterrent.
In California, you have to wait 30 days, before the actual insurance claim is made, to see if the car is recovered. That's not a fun 30 days after your "baby" has been taken.
For me, one car stolen and then one car saved with a simple and effective method, it's a no brainer.
Good Luck!
Kurt