1) If you haven't been scheduled yet - a sick day or approved time off request blocks you from being scheduled
2) If you have been scheduled - Staffjoy removes you from the shift, and other workers can claim it. (When showing available shifts to workers, we maintain compliance so that only workers eligible to take the shift can do so).
I think the more pressing question that was implied by "sick days" is what happens if nobody claims the shift before the shift starts? Sick days are often unplanned and have much less notice, so other employees may have no idea that a shift is available or it might be to short of notice for any other employee to cover it. How do (presumably) manual overrides happen in this scenario?
Right now workers can claim available shifts, and managers can assign them manually (including viewing whether an assignment may trigger overtime). More advanced shift swapping workflows will be published in the coming months too!