a high ground ball ratio seems important in the closer role, to avoid a game-tying/winning home run. Overall though, I've been surprised in the game how many blown saves there are, even by the top teams in the leagues. It seems much higher than real MLB.
I saw a post where someone was talking about HBD not having the intangible pressure of late game situations, so they use their best relievers in SUA roles, where the game puts them in to face the heart of the lineup more frequently.