A subjective evaluation is exactly what those words describe - an assessment or evaluation of something that is biased, opinionated, and even possibly highly influenced by the persons feelings.
Subjective evaluations are important because people make them all of the time, whether or not they are aware of it. For instance anytime you see another person your mind makes an opinionated assessment of them. You might or might not be aware of your unconscious assessment - maybe you make a conscious assessment of the person that is different from your unconscious one, in which case you could feel confused about the person or something.
Since earlier in this paper I stated that everything in life is actually subjective, that means that people are constantly making subjective evaluations whenever they think about anything. Any thought about something could be subjective in some way.
If you see a photograph maybe you have an unconscious opinion of that - or even if you think about something you wouldn't typically consider to be emotional your mind could still have a strong unconscious feeling or interpretation.