Difficult for evaluator to judge the overall structure and strategy of a course. Evaluators often find the presentation boring, but only because they already know the subject matter. One could also include a statement of educational philosophy, syllabi, assignments and handouts given to students, computer programs used or written, class notes or lesson plans, etc. This portfolio is examined and evaluated by other faculty. Feedback to teacher can be excellent.
Evaluators can themselves learn teaching techniques by examining portfolios.
Good separation between evaluation of teaching and evaluation of subject matter. Time consuming to evaluate the portfolio. There is a great temptation to skip over important parts. Delayed feedback to teacher. Microscopic examination of the course can ignore overall course structure and strategy.