Turrets and spinally mounted weapons

What do y'all think of having large spinally mounted weapons, then having smaller versions of the main weapon in turrets. I.e., if the main weapon is a 56 inch MAC, then the turrets carry three 18 inch MACs, and there's four turrets for better coverage? If the main weapon's a 400 megawatt laser, then the turrets have 100-150 megawatt lasers.