IMO, most vehicle manufactures are pretty conservative when it comes to chains. They will often just say don't use them instead of telling you the pros and cons and letting you make an informed decision.

Personally, I feel you should chain all four since you not only want traction, but also want to be able to steer effectively. I've been on a number of roads where vehicles without chains starting sliding sideways, and where people who were only chained in one end starting having the unchained end pivot around the chained end.

But.. You need to get a feel for how the chains apply to your specific vehicle.

For example, on our Jeep GC, there was plenty of space on the front wheels, but the rear had very little clearance between the tire and the rear shock. So obviously you were at risk to tear up the shock. In this case, I made sure we used a lightweight chain that fit well, and took care to go slow and make sure the chains didn't loosen up.

As suggested above, make sure they fit before you need them. I've found even chains marked for a given tire size may sometimes not fit correctly.

The upside is a (true) 4x4 (or good AWD) with all four tires chained can move effectively in some pretty impressive stuff. Of course you start to get in trouble when the snow is any significant depth over your ground clearance.

Good luck!

-john