Buying direct gets you all points where with a resale the owner may have used this and next year's points. Direct is immediate points where resale takes 2-3 months. Direct gets you all perks like using for cruise line,
DVC priced annual passes, access to member lounge at Epcot, special DVC events in parks....some other things. Resale has restrictions on those perks but really the only big loss is DVC priced annual passes and that may not be a big thing to you. Using points on cruises is not a good use as it takes a lot of points and you could rent those points out and use that money to pay for cruise....you get a better return that way.
The BIGGEST thing is direct costs way way way more. Unless buying a small contract and then the cost difference is not as much. Example....
Buying BWV 150...
...direct costs $165pp plus small closing costs, maybe $170-200, but you get all current use year points and forward.
...resale might cost $95 pp but may not have 2017 points. And closing costs are about $300-350 more than direct. So like paying $97 versus $165 and that's big.
But buying 50 points...
Direct is still $165 and @$125 closing costs with all points (loaded,).
Resale on smaller is more per point so 50 might be $125 with $250-300 more in closing than direct and likely to be stripped (not have current or next year points).
So like $134 resale and $165 direct. Or $6700 vs $8250. But two year's loss of points should be estimated at $1500 making it equal.
*Estimated