I don't think it's terribly special. Second brain seems to value the connections between fragments of thought over the thoughts themselves, that these connections will guide the creation or your outlook on thoughts originating from them, a focus on process rather than output, assuming that the output is the result of the process (oftentimes not true). Alternatively, when you are thinking about something, you can quickly find the related thoughts quickly by this organization that can help you advance it faster or more creatively. This assumes that your past thoughts are relevant to your future thoughts which are oftentimes not the case.
It can work well for technical topics that are not quickly outdated and usually have less transitory interpretations, but not as great for subjective things. If you want to have a consistency in your thinking, it can be helpful, but the value of that is also questionable. The last is more psychological, but if you keep getting distracted by a lot of thoughts, by putting them down there and being able to retrieve them when you want, it lets you focus more on things in the present without being distracted by them. If you are exploring a topic over a long span of time, and need to keep reorienting yourself back to the topic, it can be helpful.
It can work well for technical topics that are not quickly outdated and usually have less transitory interpretations, but not as great for subjective things. If you want to have a consistency in your thinking, it can be helpful, but the value of that is also questionable. The last is more psychological, but if you keep getting distracted by a lot of thoughts, by putting them down there and being able to retrieve them when you want, it lets you focus more on things in the present without being distracted by them. If you are exploring a topic over a long span of time, and need to keep reorienting yourself back to the topic, it can be helpful.