They were short of staff and rushed off their feet as it was, when he came in.
what "as it was" is here for?
as it was = 'already', in the sense of, as if that wasn't enough to have to deal with, and now this happens and we also have to deal with/contend with that.
We were rushed off our feet enough and then he walks in and ...
...wants to complain to one of the waitresses about the poor service he got the day before!