Personally, when I use bunkers it is mainly at the beginning of the game for a defense. I rarely get to use much strategy in my Terran games because usually when I am Terran I face my friend who is a god at SC. But in my general experience bunkers have been just for usage to protect myself until I am set up, and I use wraiths if they are Zerg and I mess with them by taking out their overlords with my wraiths. Oh and if they are Protoss and they try to take me out with carriers I love ambushing them by raiding their base right after they produce new carriers and I kill the carriers that don't even have interceptors yet. I know these are some pathetic tactics but I never have been an awesome player so I just stopped trying and I just try to hurt my opponents. Unless I'm in a team game, then I will actually try and I can take someone out with my other more useful strategies.