If standardized for the right ingredient (furostanolic sapponins), it has been shown to increase test., LH, and sperm count, but only if they were low to begin with. So, it could be taken after a prohormone cycle to bring levels back in the normal range.
You have to make sure, though, that you go with the right kind of tribulus product. Go with Fuzu by Syntrax or Tribestan by Sopharma. They are standardized correctly.