Nothing is more infuriating than a gunner that misses a chance to kill the other ship because he wanted to help whack something that the engineer was already whacking, or worse yet man a gun that isn't facing the enemy in a vain attempt to get an achievement. It's acceptable to whack something nearby in between Manticore volleys but your team cannot win if it doesn't keep up its DPS. The other ship WILL damage your ship faster than you can repair it, your job is to make sure you're doing the same to them and doing it faster. Have faith in your teammates, they'll let you know when you're needed to go into turtle mode.
It's actually why I feel a little insulted when the captain goes engineer when there's already two competent engineers, it's like they're implying you're incompetent and can't be trusted to do your own job, that you must suck so much that it's worth not being able to dodge well just to redundantly whack a part while having the ship travel in a straight line with its engines exposed.