Addressed comment

src/nested_pandas/nestedframe/core.py

@@ -342,7 +342,9 @@ def reduce(self, func, *args, **kwargs) -> NestedFrame:
         Notes
         -----
         The recommend return value of func should be a `pd.Series` where the indices are the names of the
-        output columns in the dataframe returned by `reduce`.
+        output columns in the dataframe returned by `reduce`. Note however that in cases where func
+        returns a single value there may be a performance benefit to returning the scalar value
+        rather than a `pd.Series`. 
 
         Example User Function:
         ```