it's not really a "benefit" so much as additional (overpriced) options.
if you buy direct, you have the option of trading out of the
DVC system for the "disney collection" (including disney cruises, adventures by disney and hotels like the poly or moderates like POFQ - but not hotels that already include a DVC component, so no hotel room at the WL since there is a DVC section attached). you can also trade for expensive hotels like the mandarin oriental in DC or the hotel del coronado in san diego.
but again, you are paying extra up front in order to pay extra for the cruises and hotel rooms. the points needed for an adventures by disney trip are even more formidable.
if you buy resale, you "only" have access to the DVC resorts (including aulani in hawaii, HHI and VB) plus the RCI resorts and buena vista trading company (club intrawest and club cordial resorts).
even there, i'd only recommend buying DVC for use at DVC resorts. RCI trades are a nice option, but you tend to be trading down in value.
edited to add: found this example, so i just quoted it.
the cheapest "adventures by disney" trade option is for the 6-day california tour - it's over 700 pts for 2 adults plus the $95 trade fee.
trading for a week in a hotel room at the poly in the first week of december 2013 would run 366 pts for a garden view plus the $95 trade fee...that would just about score you a 2BR theme park view villa at BLT for the same period.
both on the monorail - but one's a 1150 square feet villa with separate bed rooms, a full kitchen and washer/dryer with a theme park view vs. a hotel room with a garden view.
