Most people who try portrait lighting in a serious way have personal and external benchmarks they use to measure "better" against. On the personal level it is usually whether one combination of pose and lighting looks better to their eye than some other they've tried. On an external level they will seek to measure their results against those of others and may use the work of a photographer they admire as a benchmark to aim towards.

On a personal level their opinion is the only one that really matters, but their learning curve will depend entirely on their ability to determine what factors make one of their photos look better to their eye than another. Because their frame of reference is limited to what they know or believe to be true, it is very possible someone with more knowledge of technique might see room for improvement which they cannot.

For example, beginners usually will not consider how clothing and background affect the overall look of a photo and lack the frame of reference to know it makes a difference. If they pose a person in a white shirt on a dark background in their first attempt with lights, how are they to know a darker one would be more effective? They might discover that eventually when they shoot someone in a dark shirt and compare the results against the white one, but then again they may never compare them side-by-side or realize the cause and effect relationship between the color of the shirt and how well the face above it is seen in the photo.

There is no rule engraved on a stone tablet saying you must always avoid clothing lighter than the face on a background which is darker, but the fact that strong tonal contrast attracts the eye can be proven and that in turn explains in technical terms why the white shirt overpowers the face in the photo and a dark one will make the face the most attractive tonal area. That's exactly what I say in a critique when I see a white shirt or other light distraction on a dark background that pulls my eye away from the face in the photo.

Does it make a difference whether it is the first portrait the person has ever taken, or a pro which has been shooting for 20 years? The criticism is valid in either case because it is based on a well established technical benchmark. In the case of the first timer the reason the person is in the white shirt is, "I didn't know any better." The beginner will probably try using a dark shirt in their next photo session based on my critique, compare the results with their own eyes and decide my advice is sound.

Knowledge of technique is never a roadblock to creativity. The truly creative never let technique stand in their way because they don't value technique much. But that creates a bit of a dilemma for them and those they ask for feedback. Because they don't value technique their photo may be very creative but technically flawed. They may not even see the technical flaws because they either never understood the technique well enough to spot them. Or, they see technical flaws but view them as unimportant. Objective critique of their work using a technical baseline is either discounted as meaningless, viewed as some sort of personal attack on their creativity, or both. If you tell them, "It is a fantastic photo, but could be made better by (fill in the blank)." they don't ever seem to hear the first part.

A photo can be both creative and technically flawed. When the message it delivers overwhelms the flaws it is effective despite them. But on the other hand the same message delivered without any technical flaws would be even more effective, wouldn't it? If the technical flaws overwhelm an image like a white shirt on a dark background does both literally and figuratively,the intended message of the photo will not be delivered effectively. In either case the baseline used for the critique isn't the personal opinion of the critic, but rather the critic's baseline of techniques proven to work.