My first grade classroom has one very large board (at my request). Currently pinned to the board are the student journal entries about their moms (consisting of a picture they drew and a sentence composed by them, written down by me.) We are just starting a science unit about animal habitats so the board is going to turn into a science showcase combining student contributions, habitat posters, and learning aids. My large board is mainly used as a way to display student work: journal pages, art work, projects about subject matter we are studying, etc. Putting student work on boards is a good way to get students to interact with the board.
Another teacher uses one of her boards to display Living History picture cards, changing them out as the units change. Another teacher has used one board as a vocabulary/reading work board, as a writing prompt board, and a “learn about a country” board. With all of these ideas the teacher needs to make a point of using the board during class time.