It’s unlikely but there is a tiny possibility that a photographer might be ill, or there may be some other emergency why they can’t make it at the last minute.

It can be useful to find out what cover they have in place for if they aren’t available on the actual day.

They may have a second shooter scheduled for the day anyway, or other backup photographers on hand who can step in to cover.

They may also have a clause in their contract to hire another photographer within a certain timeframe.