There aren't too many such formal programs but in general they will make you very competitive for academic positions. They give you built-in protected research time to allow you to get papers and grants, so that when you apply for an Asst. Prof type job you will be at the top of any list. Many offer financial incentives to stay in research. There is nothing about the "PSTP" itself that does anything for your chances, really it's your ability to show you can be productive scientifically on the program's dime.