Leave ATRAC off until you need it. If you're in 4LO and get stuck, activate ATRAC and it might be enough to get you out of the situation and you know to reassess before proceeding (should you turn around, find a different line to take, etc.). If you already have ATRAC on and get stuck you don't really have a backup plan unless you have a locker.
Right, we have a steep driveway and my wife routinely needs to turn Traction Control off in her Camry in order to get up the driveway and into the garage. Remember that Traction control uses braking action on the spinning wheel and actually de-throttles (cuts power to the engine). Sometimes she needs to spin some tires (allowing them to "dig in" every so often) getting traction and gaining momentum. But in your T4R case, all you need to do is throw it in 4HI and you won't have any problems. I have seriously driven past 4Runners through 12-15 inch snowfalls in 4Hi without much trouble at all and really momentum helps but remember as someone else pointed out, 4wd allows you get going through snow faster but it does nothing to help you stop sooner. Also, short of winding up in a ditch, I doubt you will ever need 4Lo in snow. (Personally have not played with A-trac)
