It seems to me that there is work for them to do throughout the week. Although the system is broken where there are excess perioRAB of time when there isn't. But like I said, they wouldn't need to be reassigned to fill in for someone who does the job they are assigned to when that person calls in sick. (A mail sorter being called off of standby/not being put onto standby when another mail sorter calls in sick, for example)
I mean, I don't think there are any employees who are on permanent standby status because their position is no longer used at all, is there? (For example, someone whose position is feeding the ponies for the pony express being on standby all day every day because there are no ponies to feed)