While your bylaws may stipulate something else, in fact, according to Roberts Rules of Order, ex officio members of the board have the full collection of rights and privileges as do any other member of the board. Ex officio does not mean “not quite official.” It translates from Latin as “from the office.” What makes ex officio members different than regularly elected or appointed members is that they serve as a result of some office they hold.
For example, you might want the editor of your newsletter to be an ex officio member of your board. That person would be able to fully participate in board meetings and then appropriately report on the proceedings in the newsletter. Being part of the board allows that person to build different relationships and have different access than s/he might if not part of the group. But if the board decides that that editor needs to be replaced, then that person would also no longer be a member of the board of directors.
It is also common to include, or exchange, ex officio members between related but distinct organizations. For example, two chapters of a national organization that are geographically connected might benefit from access to information about what plans are each group is making.
Sometimes the president of an organization is an ex officio member of all committees of the board (with the exception of the nominating committee).