The ability to ensure every element in a column is wrapped in parentheses, or has a uniform custom unit would be very helpful. Currently Revit offers the prefix/suffix only as a feature in combined parameters, which require two parameters. This means that a extra parameter must be added (or identified) to the elements in question that is then managed to ensure it stays blank, a functional but annoying work-around. This feature probably would be easier to implement as a change to combined parameters, though it would be more uniform to offer it as an option under field formatting for every parameter.
Related to: Combined Value in Schedule Improvement