The only "practical" function of them I can find is the possibility of n-way anaphoric binding for n genders - e.g. German Er liegt zwischen ihm und ihr ('he lies between it and her') could accurately describe the placement of utensils on a dining table (der Löffel 'the spoonMASC', das Messer 'the knifeNEUT', die Gabel 'the forkFEM')... or for the confusion of 2nd-language learners. However, while some languages feature 10 or more noun classes (e.g. Bantu languages), there are a great many languages which work just fine without any.
(Granted, this argument could hold reasonably well for inflection, lexical accent, lexical tone, tense, aspect...)