None.
Primo Gucci Leather roll bags, plastic milk crates, Piaggio top cases, Vespa top cases, Shads, Givis, plywood boxes - they all spoil the otherwise sleek lines of a scooter, IMHO.
Refused them on my Forza and Burgman....but had to use them on my smaller scooters...to the detriment of their appearance.
They are useful - and can be a nice safety feature if you buy one with running & brake lights in them.....but they're ugly.
And apparently - a percentage of people buy a scooter rather than a motorcycle to haul stuff around. (I suspect it has more to do with fear of shifting)
O.S.