Are they necessary? We are NOT hosting a formal,traditonal wedding: the vibe is halfway between casual and semi-formal . Our guest count is 80-90 and we're doing an open seating with only the first 2 rows reserved for immediate family + their SO's and grand parents.
Neither of us wants to have ushers so none of our guests would have to "work". On the other hand, we don't want anyone to be confused.