The Board Chairman temporarily steps aside and lets the Vice Chairman conduct business because the Chairman has a personal interest in the matter before the body. Once the Chairman steps aside and become just another member of the body with the Vice Chair conducting business for the body, then can the Chair vote and make motions as other members of the body.
Dear James,
I suppose it depends on what a "personal interest" means. If it means he has strong opinions about something then the answer is "yes." If it means that he would gain money, business or some other benefit from the transaction, that other members would not, then he should completely step aside. He should not discuss it, make motions or vote. He should let the members completely decide this without any in put at all. Some presidents actually leave the room while the members are making a decision on something that affects the personal interest of the president. However, the official Robert's Rules Book, states that "no member can be compelled to refrain from voting in such circumstances." The best policy is to let the members decide by a motion and a ballot vote whether they want the president to participate.
Cheerio,
Little Ben
Question submitted by James on June 28, 2016