I think the problem is not extra work for staff during the procedure, with or without sedation, but the fact that with sedation the person has to be monitored afterwards for an hour or so. The type of medication can cause blood pressure to drop, so you're hooked up to a a BP monitor for a while. They need beds and staff to monitor those who have been sedated, and they may not be available.
Can't comment on what it's like without sedation as I opted to be sedated - my GP told me he had it without sedation as he had to be back at work in afternoon.