Diamond had 4 types of ownerships. 1) The most basic one is ownership of a deeded week at a specific resort without membership in the Club. 2) The Club is like an exchange program within Diamond resorts. If you join the Club and add your deeded week to the Club, Diamond give you points for that week and you can use the points to book at any resort that is also in the Club. 3) You can buy points from Diamond. The point are part of a trust or collection of a limited number of resorts. The trust owns the deeded weeks at those resorts, and you can use your points to book any resort in the collection. When you buy points from Diamond, it includes membership in the Club, so you can also use the points to book Diamond resorts outside the collection. 4) If you sell your points, the Club membership is not transferable. The buyer will only be able to use the points to book resorts within the trust's collection. Resale points are also called dirty points because you can't use them outside the collection. You can negotiate with Diamond to put the points into the Club so you can use them anywhere, but that usually requires buying more points from Diamond at their highly inflated prices. Owner's of points find them difficult to sell because the Club membership is not transferable, and because the overhead of managing the trust's collection makes the maintenance fees unusually high.
The more points you have in the Club (not counting dirty points), the higher the tier level, silver, gold, platinum, etc. There are more perks as the tier levels get higher, but Diamond can change the level thresholds and number of perks whenever they want. Confused? They want you to be confused. It's easier to talk you into buying more points. They don't sell deeded weeks anymore, but you can buy them on the resale market. If you find a Diamond property you like and you plan to go there every year, deeded weeks are the best way to go. You can also exchange deeded weeks through RCI or Interval International and deeded weeks are easier to sell. Points do have the advantage of flexibility. It's easy to book any number of days, sometimes on short notice, and there's a large variety of resorts.