Definately agree with the five sames idea.
In its basic form an aligned skier will have his skis flat when standing in a neutral position. There will be no edge engagement. Proper alignment just makes it easier for you to ski efficiently, with less energy, and enjoy the experience more.
Alignment helps by removing any tendancy to turn when the skiier is moving while in the neutral position. It also affects all other skiing positions. Its like alignment on a car. If the front wheels are pulling in different directions, it is harder to steer and control the car. I've seen cars that were so far out of alignment that they looked like they were coming down the road sideways.
If one ski is set up so that it wants to turn when the skiier is in the neutral position, the skiier will have to compensate. This will put the skiier out of position for efficient skiing. In the worst cases the individual may not even be able to ski.
I know of one individual that has bowed legs. Standing in neutral, the outside edges of his skis were engaged. Kinda makes it hard to do any flat ski stuff or even make a wedge. He was told by one ski school that he couldn't ski. He finally got to good alignment specialist (Harb) and is enjoying skiing using PMTS. He's a good skiier now and is enjoying his time on the slopes.
If you are knocked kneed your on the inside edges. This makes it harder to flatten the inside ski while turning.
There are others out there that really know what to look for on the hill. Some things I see are, edge catches, railing, inability to do flat ski work, improper stances, etc. Before I got aligned, I had a tendancy to catch the inside edge of a ski and watch it rocket off in a direction I didn't want it to go.
As an instructor of beginners, I know that most of the problems beginners are having tend to be gross motor stuff. The typical beginners learning to move those size 4000 shoes. However, I need to be aware of alignment issues. Sometimes, its not a beginner problem but an aligment problem. It doesn't happen often, but it does happen. My job on the hill is to make the skier's experience enjoyable so they will come back. If getting a skier aligned makes the experience more enjoyable then I'm doing my job.
This is especially critical to be aware of in Adaptive Instruction. I've had a student that had a twisting deformation of the tib-fib caused by CP. This twisted the foot in about 20 degrees. (It will be corrected by surgery when the leg stops growing.) The student could turn one way but not the other because the outside edge would engage instead of the inside edge as the knee was bent. In two years no one else had spotted the problem and I wouldn't have spotted it without my knowledge of alignment problems. This will require some special adaptations for the student until the surgery.
For the most part, if a recreational skiier is happy with how they are skiing and they aren't aligned, I don't care. They are happy and that's the whole point of recreational skiing. However, if they are having problems progressing and alignment will help, I'll nudge them in that direction.
Most advanced skiiers will start to notice a point when things just don't work right. This is normally at the point when they are becoming proficient. This is the time when a proper alignment will be appreciated by them.