As I remember the manual says to avoid using Auto when it's just wet, it puts unnecessary wear on the system.
I only put mine in Auto when I'm on mud, sand or snow. But as dieselglider says you need to be careful and understand how it works. The rear will kick in when it detects slip at the front. I've had occasions where I've given it too much welly on a corner, it's put power to the rear and it's put me into a massive powerslide. Fun when there's no one else around but could be game over if you're not expecting it.
Auto is amazing when going up snowy hills. It will activate the rears just as you feel you're not going to make the Hill and it gives you a nice gentle push.
Lock is a 50/50 permanent split between front and rear and makes the car incredibly capable. I've used it to get me out of snow and ice and very muddy fields on the farm (like yesterday funnily enough when a Rav4 was stuck). Again be careful with this setting, it's not meant to be used all the time and when I've had it on too long it starts to heat up and you'll get funny noises from the back. It's happened to me.
I've always been on summer tyres but living in the South it's not economical for me to get a winter set.
So the key is slow and steady. And don't use Auto and Lock for the sake of it, use it when the conditions actually need it.
Have fun, look after your Sedici!