So my question is: Why should one ever isolate and focus on twisting the ski when it is almost always more effective to tip and twist or in some cases exclusively tip the ski? I ask this question whether it is the context of a drill or real skiing. I also realize that there are a few situational exceptions where a pure twisting of the ski might be desirable – let’s try to focus on the more common skiing situations and environments, not the exceptions or drills like pivot slips.
Some support for my point of view:
Tipping engages an engineering design of the ski to bend and produce turning forces. This is true in both hard and soft snow although the mechanisms are a bit different for these two conditions. It only seems logical to want to employ this turning force to the degree possible in every turn. A point of clarification: tipping and carving are not synonymous. A tipped ski produces turning forces not matter what degree of edge lock exists, i.e. a "scarving" ski still produces turning forces.
Tipping the skis requires a much more balanced position over the skis that twisting them. If you are a position to tip the skis you can easily twist them. The vice-versa is not true. Thus tipping better encourages good balance.
Tipping the skis does not promote upper body rotation to anywhere near the extent that twisting the skis does. I understand that it is an important teaching focus to teach steering with good upper/lower body separation but this is often a difficult thing for people to achieve.
Some experiential support:
I have only taught part time for one season. However, my experience seems to support this position. I worked at Snowmass and received a lot of training in their Beginner Magic system. They asked us very specifically, as new instructors, to follow their prescribed progression. That included a focus on turning the legs and tipping the skis to initiate a turn. As I tried to employ this I saw a good percentage of my students throwing in significant upper body rotation to try and turn their skis even though we very explicitly talked about, demonstrated, and statically practiced isolation of the upper body from leg rotation. At this point (this happened in most first day lessons) I would switch to an exclusive focus on flexing for release and tipping (based on passed teaching experiences with friends and family). The results for the vast majority of my students was a dramatically improved ability to initiate and link turns, noticeable reduction in upper body rotation, and improved confidence. They still were twisting their skis some but it was in combination with active tipping. I have had similar success with a focus on tipping with upper level skiers who I have taught informally (I only was allowed to teach levels 1-4 in my first year at Snowmass except for a few privates stemming from group lessons or chair lift discussions). The most generally effective way I have found to reduce upper body rotation is a focus on release and tipping. From what I have seen this, in no way, inhibits people from additionally twisting the ski, in fact, it better sets them up to naturally add twisting of the skis via isolated leg rotation with much less guidance.