I think good documentation should help the user build a mental model. Keep explanations to the point in general, but insert short reminders about previous concepts (with cross-references to s detailed explanation) to keep them in the reader's mind. Some redundancy in documentation is a plus.

If you always include at least a summary of what the user is expected to know, it lets the user read the documentation nonlinearly without getting completely lost when they hit an unfamiliar concept.