Every year I get a flood of user support tickets about the scary notification that appears in every users client (this is also something that should be fixed) whenever the Database Encryption Key is nearing it's one year expiration. Now, obviously I should put an entry in the calendar to update the key ahead of when the notifications are going to start appearing. However, since the key lasts exactly one year from the last time it was updated, if I update the key, say, five days before expiration, then a new timer has been set, and the next time I update the key will have to be five days before that, and the next year it will be five days before that, and so on, so I can never schedule a specific date during the year to update the key, I always have to wait until I've updated it, and then schedule, as my key update time rotates slowly through the year. Also, if for some reason I'm unavailable at that time the date can bounce around. Five days lead is dangerous, if I'm out sick for a week and a half the data key will expire, so probably a couple of weeks should be the gap, meaning every two years we're shifting the update into another month.
If the lifespan was thirteen months I could make a scheduled calendar entry to update the key for the same strategically chosen time every year (remember, I have to ensure that all users are offline and all TNEW sites are in Maintenance Mode, and I'm part of a consortium). If some issue comes up, I can delay the update for several weeks and still not worry about users getting an error message, and not worry about my schedule being thrown off for next year.