I believe that the LORs are the board's opportunity to get a little more understanding about you as a person from another person's point of view. It could also be used as a means to see what kind of people are willing to speak well of you on your behalf. This is why I submitted LORs from 3 COs, a DH, and 2 DIVOs. It could possibly be used as a means for a tiebreaker when it comes down to selecting the last few people. At the end of the day, the only people who could say whether they hold value or not are people who have actually sat on a board. Surely, there's a reason for it being a requirement.