Think of PTS as an investment vehicle.  PTS along with AngelShares AGS solved the problem of how to fairly distribute a new product, aka BitShares BTSX.  Miners with CPU's and GPU's are able to mine PTS where as anyone with $ could simply purchase AngelShares directly.  PTS is a "coin" while AGS is an internal share provided by I3, not liquid.  Anyone who holds PTS or AGS during a snapshot will acquire shares in a new DAC such as people did with BTSX.  2 billion total BTSX shares were divided 50/50 between PTS and AGS holders.

BitShares BTSX is the first main DAC with a vast range of 2.0 technology.  See posts above what makes it so great.