I got to run my new LE on a poorly maintained road when I was breaking it in. It was all gravel and generally has a couple inches of hard packed ice / snow which is effectively the road surface for the winter. When I was up there though the temperatures had shot up to +12C (53F), and it was a slushy muddy mess, a great time to test out the difference between H4F and H4L. There is a noticeable difference, I was kind of surprised to be honest. I was getting a lot of slip and some fishtailing and once I flipped to H4L it was planted and stable. I would only bother with H4L if you're on a really slick surface or in very deep snow (10"+ or so) and you are feeling lateral slip of some kind.
I leave traction control on unless I'm having fun and trying to slide, Traction Control / VSC will save your butt before before you have time to pucker. I would turn if off maybe for really deep snow on a trail where I decide that I want wheel spin if I need it, but would probably never turn it off otherwise. Traction control is the best winter technology to come to vehicles in a long time. The guys with RWD BMW's and snow tires are doing fine now in Canadian winters and it's totally thanks to traction control and VSC.