Well since your asking this question then I assume you don't go offroad. With that being said if this 4runner is in the city or hwy only then I would only use your 4wd hi when it snows in seattle. However, due to gas prices I don't use my 4wd everytime it snows here in Indiana. I only use it if (there is snow) I know the road I am traveling has a few turns in it b/c its a rear wheel drive vehicle I don't wanna fish tail (unwillingly) and run off the road or slide into someone. Essentially if I'm gonna be turning the wheel at speed (lane changes and road curves). If the road has some hills (and snow) then I might engage it in 4wd before I get to the hill so that I don't get stuck mid hill and then lose all momentum. I see you're in seattle and I wouldn't engage it in 4wd in the rain. I know it doesn't rain here as much as in seattle but I've driven hwy speeds in very very hard downpours and have never needed 4wd. I would think hydroplaneing would make you feel like you need 4wd but you need to just slow down. I enage it gravel roads about once every 3 months to just engage the 4wd and keep everything lubed. With all that being said, I only engage 4wd if its necessary. With gas prices the way they are I don't see it necessary to drive in 4wd if I can be cautious and keep it in 2wd and still make my destination.