You have to vote on tenure etc.

Your dean is going to make a case for a promotion. In a large department, perhaps with a variety of specialties, it is likely that the economic types and the organizational theory types will find it hard to judge candidates in the other field. Yet the provost needs to see a vote of the faculty that indicates its support for whatever position the department takes. It's essential that all faculty who are eligible to vote actually vote. Otherwise you make it much harder for your dean to make a convincing case. It's fine if there is some dissent. That is expected. But if only half the department votes, with all voting yes, no provost will find the vote convincing.