First let me touch on this idea of "plant vs. touch".
It is greatly misunderstood in my view.
Lets start with an analogy - if you wanted to give your friend a "high five", out the window of your moving car, while he stood on the side of the road, what would happen? Lets say you just stuck your arm out, and hand up...he did the same...and as you drove by at say 20mph, your hands hit. How would this "feel"? Remember, you didn't swing your hand at all...neither did he....so it would be a gentle "touch" right? Well I am sure that most people could figure out intuitively that it would a be hard slap...equal to 20mph worth!
Skiing - we are also moving at an average speed for average skiers likely close to 20mph....so when we move our pole, even with a gentle subtle "touch" action...we will feel and impact or a "plant" due to our speed.
So what gives? What makes a touch, a plant, or a block? The angle with which the pole enters the snow relative to our direction of travel. It really has nothing to do with arm swing/effort....that is not to say you cant stab away...but it is to say, that even with a gentle hand action, you can create a full blocking plant. This would be considered the "proper" way to get a block...or touch for that matter. - the desire to maintain a calm upper body is the reason.
So when do we do what? Basically a pole plant is there to stabilize our upper body primarily in the rotational plane and to a lesser extent the lateral plane. Generally we need more rotational stability in shorter turns, and less in longer. This works out well, because in longer turns we also tend to be going faster, thus the 20mph, is now perhaps 45mph, and we don't want to rip our arm off! Hence in longer turns the pole angle is such that the pole might not even "anchor" in the snow, but rather just graze the surface. In shorter turns, where we need to rotational stability, the angle is set such that the pole does "anchor" into the snow and blocks the upper body rotation, transferring all the rotational energy into the skis, were we want it. The anchor is very very brief, fractions of a second as the pole is released as fast as it is anchored, but the brief block of the upper body is all that is required to aid the turn.