For both the Pyramidion and Goldfish, the engineer can make great use out of the side guns. On the Pyramidion, any wide-arcing weapon like the Gatling or Flamethrower can be used in a trifecta; repairs come first obviously, but if your captain manages to get in an enemy's blind spot you can GREATLY screw them over by manning that third gun, it's often an absurdly fast kill if all three guns can hit at once. On the Goldfish, in between Hwacha rounds it's possible for the pilot to do the Goldfish wiggle and bring a side Gatling or Flamethrower in arc while the Hwacha reloads; the gunner counts down until his reload to let the pilot know when to bring the front gun back up. It puts a lot of stress on the enemy engineers who need to repair enginers or the main cannon and then get distracted by the exposed hull or everything suddenly catching fire.
Those are both tactics that you can bring up to your captain if he's a bit inexperienced, otherwise if the captain makes it clear he's not going to try those maneuvers it's better to just stick to the occasional defensive pass.